diff --git a/Makefile b/Makefile
new file mode 100644
index 00000000..15710da9
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,117 @@
+# Common objective-git developer commands. Run `make help` for the list.
+#
+# Targets deliberately mirror the steps in .github/workflows/BuildPR.yml so the
+# two stay in sync; the CI step each one matches is named below.
+# Changing a command here means changing it there too, and the other way round.
+#
+#   deps      "script/bootstrap" and "script/update_libgit2"
+#   test      "Test project" (commented out in CI for now)
+#   archive   "Archive project"
+#
+# Override the architecture on an Intel Mac or for a cross build:
+#   make build ARCH=x86_64
+
+ARCH ?= $(shell uname -m)
+
+WORKSPACE := ObjectiveGitFramework.xcworkspace
+SCHEME := ObjectiveGit Mac
+DESTINATION := platform=macOS,arch=$(ARCH)
+
+LIBGIT2_ARCHIVE := External/libgit2.a
+LIBGIT2_BUILD_DIR := External/libgit2/build
+
+XCODEBUILD := xcodebuild -workspace $(WORKSPACE) -scheme "$(SCHEME)" ARCHS="$(ARCH)"
+
+MAKEFILE := $(firstword $(MAKEFILE_LIST))
+
+# Column the map target lines its descriptions up in.
+MAP_WIDTH := 24
+
+.PHONY: help map git-submodule-sync git-submodule-check deps bootstrap \
+	libgit2-clean build test archive clean git-clean-dry-run
+
+help: ## Show this help
+	@grep -hE '^[A-Za-z][A-Za-z0-9_.-]*:.*## ' $(MAKEFILE_LIST) \
+		| awk -F':.*## ' '{printf "  %-20s %s\n", $$1, $$2}'
+
+# Reads the edges out of make's own rule database, so a target that gains a
+# prerequisite appears here without anyone maintaining a second copy of the
+# graph. The descriptions alongside are the help text above, in a column.
+map: ## Show which targets pull in which, with the help text
+	@{ make -pnr -f $(MAKEFILE) 2>/dev/null \
+	   | sed -n 's/^\([a-zA-Z][A-Za-z0-9_.-]*\):\([^=]*\)$$/EDGE \1\2/p' \
+	   | grep -v '^EDGE $(MAKEFILE)' | sort -u; \
+	   sed -n 's/^\([a-zA-Z][A-Za-z0-9_.-]*\):.*## \(.*\)$$/DESC \1 \2/p' $(MAKEFILE_LIST); } \
+	| awk -v width=$(MAP_WIDTH) '$$1 == "EDGE" { target = $$2; $$1 = ""; $$2 = ""; sub(/^ +/, ""); prerequisites[target] = $$0; order[++found] = target; next } \
+	       $$1 == "DESC" { target = $$2; $$1 = ""; $$2 = ""; sub(/^ +/, ""); description[target] = $$0; next } \
+	       function label(indent, name,   left) { \
+	           left = indent name; \
+	           return (name in description ? sprintf("%-" width "s - %s", left, description[name]) : left) \
+	       } \
+	       function walk(name, indent,   i, count, needs) { \
+	           count = split(prerequisites[name], needs, " "); \
+	           for (i = 1; i <= count; i++) { print label(indent "\\_ ", needs[i]); walk(needs[i], indent "   ") } \
+	       } \
+	       END { \
+	           if (found == 0) exit 1; \
+	           print "Make Targets Map _______________________________________________________________"; print ""; \
+	           print "Targets that pull something in _________"; print ""; \
+	           for (i = 1; i <= found; i++) if (prerequisites[order[i]] != "") { print label("", order[i]); walk(order[i], ""); print "" } \
+	           print "Targets that stand alone _______________"; print ""; \
+	           for (i = 1; i <= found; i++) if (prerequisites[order[i]] == "") print label("", order[i]) \
+	       }' \
+	|| { echo "map: no targets found in $(MAKEFILE)" >&2; exit 1; }
+
+git-submodule-sync: ## Check out the submodules at the revisions this tree wants
+	git submodule sync --recursive
+	git submodule update --init --recursive
+
+# Locally this warns and carries on, since parking a submodule on a commit of
+# your own is a normal thing to be doing. On CI the checkout step is the only
+# thing that puts submodules in place, so there drift fails the build.
+#
+# GitHub reads its annotations from stdout, and %0A is how one carries a
+# newline.
+git-submodule-check: ## Report a submodule that is not at the revision this tree wants
+	@drifted=$$(git submodule status --recursive 2>/dev/null | grep '^[+-]'); \
+	test -n "$$drifted" || exit 0; \
+	list=$$(echo "$$drifted" | awk '/^-/ { print $$2 " is not checked out"; next } \
+		{ print $$2 " is at " substr($$1, 2, 8) }'); \
+	if [ -n "$$GITHUB_ACTIONS" ]; then \
+		summary="the checkout left submodules that are not at the recorded revisions"; \
+		echo "::error title=Submodule drift::$$(printf '%s\n%s\n' "$$summary" "$$list" \
+			| awk '{ printf "%s%s", separator, $$0; separator = "%0A" }')"; \
+		{ echo "error: $$summary:"; echo "$$list" | sed 's/^/  /'; } >&2; \
+		exit 1; \
+	fi; \
+	{ echo "warning: submodules are not at the revisions this tree wants:"; \
+	  echo "$$list" | sed 's/^/  /'; \
+	  echo 'run `make git-submodule-sync` to check them out'; } >&2
+
+deps: ## Install the Homebrew tools and build libgit2
+	script/bootstrap
+	script/update_libgit2
+
+bootstrap: deps ## (alias)
+
+libgit2-clean: ## Drop the built libgit2 so the next deps or build rebuilds it
+	rm -rf $(LIBGIT2_ARCHIVE) $(LIBGIT2_ARCHIVE).stamp $(LIBGIT2_BUILD_DIR)
+
+build: git-submodule-check ## Build the macOS framework
+	$(XCODEBUILD) -destination "$(DESTINATION)" build
+
+test: git-submodule-check ## Run the macOS framework specs
+	$(XCODEBUILD) -destination "$(DESTINATION)" test
+
+archive: git-submodule-check ## Build a release archive of the macOS framework
+	$(XCODEBUILD) archive
+
+clean: ## Remove the libgit2 build and Xcode's build products
+	$(MAKE) --no-print-directory libgit2-clean
+	$(XCODEBUILD) clean
+
+# Lists only, and nothing depends on it: the real `git clean -Xdf` throws away
+# every ignored file in the tree, not just the ones a build made, so deciding
+# to run it is left to you.
+git-clean-dry-run: ## List the ignored files a `git clean -Xdf` would remove
+	git clean -Xdn
diff --git a/README.md b/README.md
index ba694c55..ddcc8885 100644
--- a/README.md
+++ b/README.md
@@ -46,6 +46,7 @@ Homebrew, you will need to install the following manually:
   - symlinks:  lib/libssh2.a include/libssh2.h include/libssh2_sftp.h include/libssh2_publickey.h
 
 To develop ObjectiveGit on its own, open the `ObjectiveGitFramework.xcworkspace` file.
+From the command line, run `make help` to list the targets that bootstrap, build, test and archive the framework.
 
 # Installation