Is Alien Arena still being developed?

Yes, it certainly is: introducing Project 100, supporting the smoothest Alien Arena gameplay experience yet!

The game engine and net code have had many improvements to fully support a smooth and responsive game experience for at least 100 FPS framerate, 100 FPS server tickrate, 100 PPS packet rate for client-server communication, and mouse polling that scales with your framerate (100 Hz at 100 FPS, 200 Hz at 200 FPS, etc.).

With this, the gameplay should remain smooth even with older hardware or high ping, now fully lifting the game from its Quake 2 legacy of 10 server ticks per second to a modern game.

Along with this, we've also improved the lag compensation.

This will become available in the next release: 7.72. Along with many other improvements and bug fixes to aim for 100% stability.

You are welcome to beta test the updated servers or, for the most optimal performance and responsiveness, also the latest client code.

To play using the new client, we currently support only Linux, Windows users need to wait a bit until the official release of 7.72. But will already benefit from the updated servers!

Linux users can download the latest source code from SVN or GitHub and then build the client:
https://svn.icculus.org/alienarena
https://github.com/alienarena/alienarena

How to build the executable in detail is explained on https://www.alienarena.org

Project 100 is now available for Linux users on Flathub: https://flathub.org/en/apps/org.alienarena.alienarena