gamescope (SteamOS session compositing window manager)

the micro-compositor formerly known as steamcompmgr

GameScope is a tool from Valve that allows for games to run in an
isolated Xwayland instance and supports AMD, Intel, and Nvidia GPUs.

(Nvidia and Intel GPUs may be unsupported with this version, but I
do not have the hardware to test.)

NOTE: gamescope version 3.8.4 is the latest version that can run on
Slackware 15.0 due to older vulkan headers and wayland-server. Newer
versions might run on -current, but due to the very large number of
git submodules that have been added to the project since this release,
it might be easier to clone the project and build it manually using
the instructions on their git page.