Spine is an upcoming PlayStation 4 emulator that's currently closed-source while it's under heavy development. It's also currently only available for Linux. Well-known PlayStation "scener" Nagatoro announced the new demo on Twitter along with a download link.
What's interesting is that the PS4 was the generation to come back to x86 CPUs, instead of the Cell style found in the PS3. This makes the emulator a bit more like the Wine compatibility layer and less like a full emulator, the developers even announced it originally as it being "Wine-like".
The readme doesn't contain much right now:
spine version 2021/09/01
made by spinedev
compatibility list (rudimentar, please improve it) in compatibility.xlsx
please include firmware dependencies in firmware folder
for linux only. for ubuntu it's required to install libsdl2-dev, rest of libs are available in lib folder
chmod a+x both lib folder contents and spine executable, then you can place these contents in your game folder and type
fself eboots are supported
arrow keys to move (dpad)
zxcvb etc keys should be for triangle, square, circle, cross, options, etc
undertale works really well as well as we are doomed, others ingame may experience some graphical glitches and artifacts
Compatibility has come on massively though with many titles now able to actually get in-game. The included compatibilty list has 996 titles listed with 345 mentioning the go in-game and 207 that don't work at all yet.
It's not a particularly easy project to follow since the developer keeps to themselves. They are on Reddit occasionally, and they seem to have no plans to bring Spine to Windows. When asked why it was Linux exclusive the developer replied to say:
It makes some things a bit easier but the primary reason is that's the system I use. It could be made to work with some effort (I had a limited macOS version for a while for example) but frankly I don't really care. Especially with the direction Windows seems to be going, I probably won't even be upgrading to 11.
They also confirmed they still plan to open source it eventually and it's at a point now where they can make new releases "fairly easily".