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).
"Isn't weird a rude way to refer to games?" H*ck no! If it ain't weird, it's...something bad that rhymes with weird. Weird is a word that lets me explain that these are something different, offbeat, unique, or avant garde, without cramming all that in a title. It's definitely not an insult.