Phun

Phun is a 2D sandbox physics game where you can build almost anything by using hinges motors and shapes. It's not quite done but you can learn more and download it for free here.

Audiosurf

Audiosurf is a rhythm based game that generates tracks based off the song you want to surf. You collect colored blocks and build matches to gain points. The objective is to have fun and try to get the highest score on that song. Learn more about Audiosurf here. It's available for purchase on steam for $10.

I Wanna Be The Guy

I wanna be the guy is and extremely difficult platforming game. It was inspired by an extremely difficult game the developer found on 2chan and he thought he could do better. The game is still kinda buggy but you can learn more and download it for free here.

OE-Cake
Cake is a fluid simulator similar to games like falling sand, buring sand, or powder game(my favorite out of those 3). An official website might be better but there are a lot of screenshots and a lot of information in this thread(sorry if you have to read a lot).

Here's a video of Audiosurf.