When starting this normally, you would be forgiven in thinking it is a straightforward clone of Sokoban. Push the boxes onto the spots, move onto the next level, yawn. Or rage, depending on how much you get into it, and how many boxes get stuck on walls/corners/each other.
But then you check the level subset menu and see an option for 'Cyberbox':
And the rules change. Now it's a clone of an entirely different game! Now you can push multiple 'sliders' at once based on arrow direction, and the goal is only to reach the destination. A variety of new mechanics are showing up, but ultimately it's still a clone of someone else's work (Doug Beeferman, in this case).
Then you remember there was a third 'Xsok' option:
And here things start to get a bit out of control. Sokoban-style boxes start showing up along-side Cyberbox-style sliders and a bunch of entirely new mechanics. Your strength can be sapped so you can no longer push certain types of boxes, or can be boosted to push more than normal. Teleporters are now added, along with rotation arrows and so forth. It can be difficult to come to grips with, and some of the puzzles are a little bit unhinged, but it's certainly not a clone any more.
Xsok was written by Michael Bischoff in 1994 directly using and targeting Linux, so no obscure Unix variants here. The latest version (1.02) is from 1996, and there does not appear to have been any development since.
The following video is a demonstration of me playing through the first level of the Xsok-specific level set:
XSok is still bundled in Debian. If you are not on a Debian-derived distro, and your distro does not package it, you should be able to re-build the Debian source package.
Also, since the game comes with a LaTeX-based manual, but nobody bothers to generate output for it, I've also done that and uploaded it here.
More general information on old X games, including build tips can be found in the Old X Games article.
If the above video does not work for you, it is also available on my YouTube channel.