Wolfenstein: Enemy Territory's entire source code was released under the GNU General Public License v3 on 12th August 2010, and has a Linux executable download on the page:
https://www.splashdamage.com/games/wolfenstein-enemy-territory/
https://github.com/id-Software/Enemy-Territory

Yeah sadly the native linux/mac versions of id games never got added to Steam.

Pray for ET: Legacy to get the same treatment as RealRtCW!

Yeah sadly the native linux/mac versions of id games never got added to Steam.
But why would it be too late though? It's right there.

Yeah sadly the native linux/mac versions of id games never got added to Steam.
But why would it be too late though? It's right there.
Because Microsoft literally bought them.

>linux

uh... use proton my guy

uh... use proton my guy :blankstare:
Sure, but native is the preference. Why not?

ET:L has native linux engine
https://www.etlegacy.com/download

+1

A lot of these games that have Linux native versions, official or otherwise, that aren't published on Steam are supported by Luxtorpeda. It can easily be installed through the ProtonUp-Qt tool and then after restarting Steam it will appear in the list of compatibility tools. Just set it on any supported game and the Linux version will work much like it came from Steam.
In this case, when launching the game, it provides options between ET: Legacy (32 or 64-bit) or ETe (32-bit).
One exception I've noticed is that the project doesn't support reverse engineered ports such as OpenJKDF2 (Jedi Knight: Dark Forces II) since it's legally questionable. Not an issue here since the original engine was open sourced.
Luxtorpeda:
https://github.com/luxtorpeda-dev/luxtorpeda
Supported games:
https://luxtorpeda-dev.github.io
ProtonUp-Qt:
https://davidotek.github.io/protonup-qt

The old native Linux executable probably wouldn't run on our modern Linux systems. Using one of the open source ports is your best option on Linux or Windows.
Luxtorpeda makes it easy on Linux to install a native open source engine port.