diff --git a/.github/actions/install_nim/action.yml b/.github/actions/install_nim/action.yml
index 14da7d613..87c855543 100644
--- a/.github/actions/install_nim/action.yml
+++ b/.github/actions/install_nim/action.yml
@@ -117,14 +117,14 @@ runs:
       run: |
         rm -rf nim
         export NIMBLE_DIR=$HOME/.nimble
-        curl -O -L -s -S https://raw.githubusercontent.com/status-im/nimbus-build-system/master/scripts/build_nim.sh
+        cp ./scripts/build_nim.sh .
         env MAKE="${MAKE_CMD} -j${ncpu}" ARCH_OVERRIDE=${PLATFORM} NIM_COMMIT=${{ inputs.nim_branch }} \
           QUICK_AND_DIRTY_COMPILER=1 QUICK_AND_DIRTY_NIMBLE=1 CC=gcc \
           bash build_nim.sh nim csources ${NIMBLE_DIR} NimBinaries
-        nimble install nimble -y
-        ls -la nim/bin
-        rm -rf nim/bin/nimble.exe
-        ln -s $NIMBLE_DIR/bin/nimble.cmd nim/bin/nimble.cmd
-        ls -la nim/bin
-        find / -name nimble.exe
+#        nimble install nimble -y
+#        ls -la nim/bin
+#        rm -rf nim/bin/nimble.exe
+#        ln -s $NIMBLE_DIR/bin/nimble.cmd nim/bin/nimble.cmd
+#        ls -la nim/bin
+#        find / -name nimble.exe
 
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 54992a76a..c8d45eafe 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -24,24 +24,24 @@ jobs:
       fail-fast: false
       matrix:
         target:
-#          - os: linux
-#            cpu: amd64
-#          - os: linux
-#            cpu: i386
-#          - os: macos
-#            cpu: amd64
+          - os: linux
+            cpu: amd64
+          - os: linux
+            cpu: i386
+          - os: macos
+            cpu: amd64
           - os: windows
             cpu: amd64
         branch: [version-1-6]
         include:
-#          - target:
-#              os: linux
-#            builder: ubuntu-20.04
-#            shell: bash
-#          - target:
-#              os: macos
-#            builder: macos-12
-#            shell: bash
+          - target:
+              os: linux
+            builder: ubuntu-20.04
+            shell: bash
+          - target:
+              os: macos
+            builder: macos-12
+            shell: bash
           - target:
               os: windows
             builder: windows-2019
diff --git a/scripts/build_nim.sh b/scripts/build_nim.sh
new file mode 100644
index 000000000..0e0db11f9
--- /dev/null
+++ b/scripts/build_nim.sh
@@ -0,0 +1,288 @@
+#!/usr/bin/env bash
+# used in Travis CI and AppVeyor scripts
+
+# Copyright (c) 2018-2020 Status Research & Development GmbH. Licensed under
+# either of:
+# - Apache License, version 2.0
+# - MIT license
+# at your option. This file may not be copied, modified, or distributed except
+# according to those terms.
+
+set -e
+
+# Git commits
+: ${CSOURCES_V1_COMMIT:=a8a5241f9475099c823cfe1a5e0ca4022ac201ff}
+: ${CSOURCES_V2_COMMIT:=86742fb02c6606ab01a532a0085784effb2e753e}
+: ${CSOURCES_V1_REPO:=https://github.com/nim-lang/csources_v1.git}
+: ${CSOURCES_V2_REPO:=https://github.com/nim-lang/csources_v2.git}
+
+# After this Nim commit, use csources v2
+: ${CSOURCES_V2_START_COMMIT:=f7c203fb6c89b5cef83c4f326aeb23ef8c4a2c40}
+: ${NIMBLE_COMMIT:=3575fd54a890d910ace56678aa74b4237d604175} # 0.14.2
+# NIM_COMMIT could be a (partial) commit hash, a tag, a branch name, etc. Empty by default.
+NIM_COMMIT_HASH="" # full hash for NIM_COMMIT, retrieved in "nim_needs_rebuilding()"
+
+# script arguments
+[[ $# -ne 4 ]] && { echo "Usage: $0 nim_dir csources_dir nimble_dir ci_cache_dir"; exit 1; }
+NIM_DIR="$1"
+CSOURCES_DIR="$2" # can be relative to NIM_DIR
+NIMBLE_DIR="$3" # can be relative to NIM_DIR
+CI_CACHE="$4"
+
+## env vars
+# verbosity level
+[[ -z "$V" ]] && V=0
+[[ -z "$CC" ]] && CC="gcc"
+# to build csources in parallel, set MAKE="make -jN"
+[[ -z "$MAKE" ]] && MAKE="make"
+# for 32-bit binaries on a 64-bit host
+UCPU=""
+[[ "$ARCH_OVERRIDE" == "x86" ]] && UCPU="ucpu=i686"
+[[ -z "$NIM_BUILD_MSG" ]] && NIM_BUILD_MSG="Building the Nim compiler"
+[[ -z "$QUICK_AND_DIRTY_COMPILER" ]] && QUICK_AND_DIRTY_COMPILER=0
+[[ -z "$QUICK_AND_DIRTY_NIMBLE" ]] && QUICK_AND_DIRTY_NIMBLE=0
+
+# Windows detection
+if uname | grep -qiE "mingw|msys"; then
+	ON_WINDOWS=1
+	EXE_SUFFIX=".exe"
+	# otherwise it fails in AppVeyor due to https://github.com/git-for-windows/git/issues/2495
+	GIT_TIMESTAMP_ARG="--date=unix" # available since Git 2.9.4
+else
+	ON_WINDOWS=0
+	EXE_SUFFIX=""
+	GIT_TIMESTAMP_ARG="--date=format-local:%s" # available since Git 2.7.0
+fi
+
+NIM_BINARY="${NIM_DIR}/bin/nim${EXE_SUFFIX}"
+MAX_NIM_BINARIES="10" # Old ones get deleted.
+
+nim_needs_rebuilding() {
+	REBUILD=0
+	NO_REBUILD=1
+
+	if [[ ! -e "$NIM_DIR" ]]; then
+		# Shallow clone, optimised for the default NIM_COMMIT value.
+		git clone -q --depth=1 https://github.com/status-im/Nim.git "$NIM_DIR"
+	fi
+
+	pushd "${NIM_DIR}" >/dev/null
+	if [[ -n "${NIM_COMMIT}" ]]; then
+		# support old Git versions, like the one from Ubuntu-18.04
+		git restore . 2>/dev/null || git reset --hard
+		if ! git checkout -q ${NIM_COMMIT} 2>/dev/null; then
+			# Pay the price for a non-default NIM_COMMIT here, by fetching everything.
+			# (This includes upstream branches and tags that might be missing from our fork.)
+			git remote add upstream https://github.com/nim-lang/Nim
+			git fetch --all --tags --quiet
+			git checkout -q ${NIM_COMMIT}
+		fi
+		# In case the local branch diverged and a fast-forward merge is not possible.
+		git fetch || true
+		git reset -q --hard origin/${NIM_COMMIT} 2>/dev/null || true
+		# In case NIM_COMMIT is a local branch that's behind the remote one it's tracking.
+		git pull -q 2>/dev/null || true
+		git checkout -q ${NIM_COMMIT}
+		# We can't use "rev-parse" here, because it would return the tag object's
+		# hash instead of the commit hash, when NIM_COMMIT is a tag.
+		NIM_COMMIT_HASH="$(git rev-list -n 1 ${NIM_COMMIT})"
+	else
+		# NIM_COMMIT is empty, so assume the commit we need is already checked out
+		NIM_COMMIT_HASH="$(git rev-list -n 1 HEAD)"
+	fi
+	popd >/dev/null
+
+	if [[ -n "$CI_CACHE" && -d "$CI_CACHE" ]]; then
+		cp -a "$CI_CACHE"/* "$NIM_DIR"/bin/ || true # let this one fail with an empty cache dir
+	fi
+
+	# Delete old Nim binaries, to put a limit on how much storage we use.
+	for F in "$(ls -t "${NIM_DIR}"/bin/nim_commit_* 2>/dev/null | tail -n +$((MAX_NIM_BINARIES + 1)))"; do
+		if [[ -e "${F}" ]]; then
+			rm "${F}"
+		fi
+	done
+
+	# Compare the last built commit to the one requested.
+	# Handle the scenario where our symlink is manually deleted by the user.
+	if [[ -e "${NIM_DIR}/bin/last_built_commit" && \
+	-e "${NIM_DIR}/bin/nim${EXE_SUFFIX}" && \
+	"$(cat "${NIM_DIR}/bin/last_built_commit")" == "${NIM_COMMIT_HASH}" ]]; then
+		return $NO_REBUILD
+	elif [[ -e "${NIM_DIR}/bin/nim_commit_${NIM_COMMIT_HASH}" ]]; then
+		# we built the requested commit in the past, so we simply reuse it
+		rm -f "${NIM_DIR}/bin/nim${EXE_SUFFIX}"
+		ln -s "nim_commit_${NIM_COMMIT_HASH}" "${NIM_DIR}/bin/nim${EXE_SUFFIX}"
+		echo ${NIM_COMMIT_HASH} > "${NIM_DIR}/bin/last_built_commit"
+		return $NO_REBUILD
+	else
+		return $REBUILD
+	fi
+}
+
+build_nim() {
+	echo -e "$NIM_BUILD_MSG"
+	[[ "$V" == "0" ]] && exec &>/dev/null
+
+	# working directory
+	pushd "$NIM_DIR"
+
+	if grep -q skipIntegrityCheck koch.nim; then
+		# Run Nim buildchain
+		. ci/funs.sh
+		NIMCORES=1 nimBuildCsourcesIfNeeded $UCPU
+		bin/nim c --noNimblePath --skipUserCfg --skipParentCfg --warnings:off --hints:off koch
+		./koch --skipIntegrityCheck boot -d:release --skipUserCfg --skipParentCfg --warnings:off --hints:off
+		if [[ "${QUICK_AND_DIRTY_COMPILER}" == "0" ]]; then
+			# We want tools
+			./koch tools -d:release --skipUserCfg --skipParentCfg --warnings:off --hints:off
+		elif [[ "${QUICK_AND_DIRTY_NIMBLE}" != "0" ]]; then
+			# We just want nimble
+			./koch nimble -d:release --skipUserCfg --skipParentCfg --warnings:off --hints:off
+		fi
+	else
+		# Custom buildchain for older versions
+		# TODO Remove this once the default NIM_COMMIT supports `--skipIntegrityCheck`
+		# We will still be able to compile older versions by removing the flag,
+		# which will just waste a bit of CPU
+
+		# Git repos for csources and Nimble
+		if [[ ! -d "$CSOURCES_DIR" ]]; then
+			if git merge-base --is-ancestor $CSOURCES_V2_START_COMMIT $NIM_COMMIT_HASH; then
+			  CSOURCES_REPO=$CSOURCES_V2_REPO
+			  CSOURCES_COMMIT=$CSOURCES_V2_COMMIT
+			else
+			  CSOURCES_REPO=$CSOURCES_V1_REPO
+			  CSOURCES_COMMIT=$CSOURCES_V1_COMMIT
+			fi
+
+			mkdir -p "$CSOURCES_DIR"
+			pushd "$CSOURCES_DIR"
+			git clone $CSOURCES_REPO .
+			git checkout $CSOURCES_COMMIT
+			popd
+		fi
+		if [[ "$CSOURCES_DIR" != "csources" ]]; then
+			rm -rf csources
+			ln -s "$CSOURCES_DIR" csources
+		fi
+
+		if [[ ! -d "$NIMBLE_DIR" ]]; then
+			mkdir -p "$NIMBLE_DIR"
+			pushd "$NIMBLE_DIR"
+			git clone https://github.com/nim-lang/nimble.git .
+			git checkout $NIMBLE_COMMIT
+			# we have to delete .git or koch.nim will checkout a branch tip, overriding our target commit
+			rm -rf .git
+			popd
+		fi
+		if [[ "$NIMBLE_DIR" != "dist/nimble" ]]; then
+			mkdir -p dist
+			rm -rf dist/nimble
+			ln -s ../"$NIMBLE_DIR" dist/nimble
+		fi
+
+		# bootstrap the Nim compiler and build the tools
+		rm -f bin/{nim,nim_csources}
+		pushd csources
+		if [[ "$ON_WINDOWS" == "0" ]]; then
+			$MAKE $UCPU clean
+			$MAKE $UCPU LD=$CC
+		else
+			$MAKE myos=windows $UCPU clean
+			$MAKE myos=windows $UCPU CC=gcc LD=gcc
+		fi
+		popd
+		if [[ -e csources/bin ]]; then
+			rm -f bin/nim bin/nim_csources
+			cp -a csources/bin/nim bin/nim
+			cp -a csources/bin/nim bin/nim_csources
+			rm -rf csources/bin
+		else
+			cp -a bin/nim bin/nim_csources
+		fi
+		if [[ "$QUICK_AND_DIRTY_COMPILER" == "0" ]]; then
+			sed \
+				-e 's/koch$/--warnings:off --hints:off koch/' \
+				-e 's/koch boot/koch boot --warnings:off --hints:off/' \
+				-e '/nimBuildCsourcesIfNeeded/d' \
+				build_all.sh > build_all_custom.sh
+			sh build_all_custom.sh
+			rm build_all_custom.sh
+		else
+			# Don't re-build it multiple times until we get identical
+			# binaries, like "build_all.sh" does. Don't build any tools
+			# either. This is all about build speed, not developer comfort.
+			bin/nim_csources \
+				c \
+				--compileOnly \
+				--nimcache:nimcache \
+				-d:release \
+				--skipUserCfg \
+				--skipParentCfg \
+				--warnings:off \
+				--hints:off \
+				compiler/nim.nim
+			bin/nim_csources \
+				jsonscript \
+				--nimcache:nimcache \
+				--skipUserCfg \
+				--skipParentCfg \
+				compiler/nim.nim
+			cp -a compiler/nim bin/nim1
+			# If we stop here, we risk ending up with a buggy compiler:
+			# https://github.com/status-im/nimbus-eth2/pull/2220
+			# https://github.com/status-im/nimbus-eth2/issues/2310
+			bin/nim1 \
+				c \
+				--compileOnly \
+				--nimcache:nimcache \
+				-d:release \
+				--skipUserCfg \
+				--skipParentCfg \
+				--warnings:off \
+				--hints:off \
+				compiler/nim.nim
+			bin/nim1 \
+				jsonscript \
+				--nimcache:nimcache \
+				--skipUserCfg \
+				--skipParentCfg \
+				compiler/nim.nim
+			rm -f bin/nim
+			cp -a compiler/nim bin/nim
+			rm bin/nim1
+
+			# Do we want Nimble in this quick build?
+			if [[ "${QUICK_AND_DIRTY_NIMBLE}" != "0" ]]; then
+				bin/nim c -d:release --noNimblePath --skipUserCfg --skipParentCfg dist/nimble/src/nimble.nim
+				mv dist/nimble/src/nimble bin/
+			fi
+		fi
+	fi
+
+	if [[ "$QUICK_AND_DIRTY_COMPILER" == "0" || "${QUICK_AND_DIRTY_NIMBLE}" != "0" ]]; then
+		# Nimble needs a CA cert
+		rm -f bin/cacert.pem
+		curl -LsS -o bin/cacert.pem https://curl.se/ca/cacert.pem || echo "Warning: 'curl' failed to download a CA cert needed by Nimble. Ignoring it."
+	fi
+
+	# record the built commit
+	echo ${NIM_COMMIT_HASH} > bin/last_built_commit
+
+	# create the symlink
+	mv bin/nim bin/nim_commit_${NIM_COMMIT_HASH}
+	ln -s nim_commit_${NIM_COMMIT_HASH} bin/nim${EXE_SUFFIX}
+
+	# update the CI cache
+	popd # we were in $NIM_DIR
+	if [[ -n "$CI_CACHE" ]]; then
+		rm -rf "$CI_CACHE"
+		mkdir "$CI_CACHE"
+		cp "$NIM_DIR"/bin/* "$CI_CACHE"/
+	fi
+}
+
+if nim_needs_rebuilding; then
+	build_nim
+fi