Platforms: Windows, Mac, Linux
Distribution: Desura, DRM-Free, direct from developer
I picked this one up a long time ago and had a lot of fun with it. I'm still not entirely sure it's finished, but it's certainly very playable. It's more or less a silly physics platformer masquerading as a minigolf game, and the combination works wonders; it's tons of fun to smash balls around and interact with the environments in different ways. And there are all kinds of things to interact with too in the game's dynamic environments; chains and ropes, small animals, spike pits, water, and a variety of ball abilities, to name a few.
Now I know it's only $4 and IGS wants to only feature games $5 or more, but I thought I'd suggest it anyway because it's a really overlooked game and could use the popularity boost.
"Metagolf is a mini-golf game with multiple challenges. Up to 4 players can compete on the same screen, sharing the same golf ball and the same goals. Team up for loads of fun with friends or play alone to improve the accuracy of your swing across 3 different platforms (Windows, Mac Os X and Linux). More focused on action and real time strategies than a traditional mini-golf, discover full interactive environments from fish ponds to breakable chains and deadly traps. Thanks to his built-in level editor, you can create, share and download new courses. Currently available in two languages, English and French, Metagolf let you reuse any provided content or make new one from various media to create your very own world. Change the realistic physical system behaviour or combine any game mode with exiting different type of golf ball. The choice of setting your own game play preferences is entirely yours!"