The sources for ReScript's fork of Ninja are now a part of the compiler repo (see https://github.com/rescript-lang/rescript-compiler/tree/master/ninja).
Please create any new issues or PRs directly in the compiler repo.
Ninja is a small build system with a focus on speed. https://ninja-build.org/
See the manual -- https://ninja-build.org/manual.html or doc/manual.asciidoc included in the distribution -- for background and more details.
Binaries for Linux, Mac, and Windows are available at https://github.com/ninja-build/ninja/releases Run './ninja -h' for Ninja help.
To build your own binary, on many platforms it should be sufficient to
just run ./configure.py --bootstrap; for more details see HACKING.md.
(Also read that before making changes to Ninja, as it has advice.)
Installation is not necessary because the only required file is the resulting ninja binary. However, to enable features like Bash completion and Emacs and Vim editing modes, some files in misc/ must be copied to appropriate locations.
If you're interested in making changes to Ninja, read HACKING.md first.