Not necessarily "alt games" but just cool, weird stuff you never thought you'd see. Many are free, all are worth your time.
Some are more experimental than others, I'll try and note whenever a game should be treated as such (very short, no ending, no point etc).
Puzzle game operated entirely by your mouse with a lovely abstract style
Interesting procedural coastline generator, oddly amusing to just soom in and see the "detail"
Its and bits of weird games to sift through and play at your lesiure. All unfinished but at least weird enough to be interesting.
A pure exploration game with no dialog! May take you a half hour-hour to find most things. Adorable pixel art style. Could have used music a bit better but when the music kicks in it's good.
A chill audioscape to float around in as you enjoy the music.
A very 90s office simulator with lots of old tech and pop culture references. Oddly amusing extremely-low-fi sound effects. Surprisingly amusing. Takes about a half hour per playthrough.
A chill ambience machine where you make the ambient music. And it sounds pretty good even if you're really bad at composing music! A perfect game to relax in.
A cool VERY tiny beach walk 'em up with chill music and some fun text.
A gloomy hellscape of a low-res world. No objective (that I saw), fun to wander around in for 10-30 minutes. Impressive asset resuse from Grave Apologies, you can see the basic structures in the earlier Grave Appologies but it feels like a whole different game. Very interesting and ominous.