Ctesiphon

You play Ethelyn Dax, Galactic Bounty Hunter extraordinaire. Finally settling in for a long-awaited vacation on the resort world of Ctesiphon, the moment is ruined by the surprise arrival of the Black Death mercenary company.

Taking the capital city and every surrounding resort hostage as part of a payment dispute, the mercenaries expected to meet no physical resistance.
Ethelyn would be perfectly content to simply get her money back and leave the resort to sort things out with the mercenaries themselves, but as it turns out the force is led by a shadow from Ethelyn's own past that she can't simply let get away.

The Black Death mercenaries have brought so many troops, clones, drones, and mechs that they expect absolutely no resistance from the resort patrons. You will prove that complacency unfounded.
Take advantage of the mercenaries' inattention with Ethelyn's trusty Data-Spike, perforate them with the versatile Submachinegun, blast them around corners with the Gyrobuster's homing minirockets, or bring out the Jetgun to cut through heavy armor as if it were mere paper.
Ethelyn is highly nimble and can run circles around most enemies who will have to resort to overwhelming force to try and stop you. The game features seven mainline levels built in a non-linear layout allowing you to flank enemies and search for secrets.

Made in bits and pieces over the course of nearly a decade by a single developer on Linux using C/C++, OpenGL, and open-source Quake mapping tools, Ctesiphon's custom engine allows for the game to run reliably on low-spec systems. It's built to withstand large firefights with dozens of enemies, hundreds of blood spatter and bullet impact decals, and piles of giblets and scrap as you blow the enemies apart into clouds of particles and debris.

Ctesiphon has been developed on Linux first and supports virtually all controllers connected to it. On Windows only XInput-compatible controllers are supported natively, but others will work fine with SteamInput enabled. The big exception is for the Steam Deck and Steam Controllers, these won't be natively supported on Linux/SteamOS until after release but in the meantime they should work fine if you play the Windows build by setting compatibility to any version of Proton.