There were some forks and merges already back then that probably did not help. Then Canoncial hired the main dev, with the main project not surviving far beyond his later departure. Official end point for the project seems to have been https://www.phoronix.com/news/MTI2ODU, in 2012 and mentioning Wayland as reason (as if that were anywhere close back then).

But actually, the launchpad repo has recent commits (or do I read https://code.launchpad.net/~compiz-team/compiz/+git/compiz/+... wrong), and so does https://github.com/compiz-reloaded. You can still just use one of those if you want - Void Linux for example has it packaged, and so does Ubuntu.

Worth mentioning that https://wayfire.org/ is a spiritual successor that runs in Wayland.

It's still around but not in active development. Tiling window managers like i3 are just a window manager, but you can add compiz as your compositor to wobble if you want. I think compton is still the most popular "just good enough" compositor used by i3 users (it's what I use). Sway is both a compositor and a window manager.

Well I have some great news for you if you're running plain Gnome today. You need this! https://extensions.gnome.org/extension/4679/burn-my-windows/