Similar in concept to the Total Perspective Vortex, from Hitchhiker's Guide to the Galaxy, The Scale of the Universe 2 isn't really a game, but it'll still blow your mind. You start at human scale and can scroll all the way down to theoretical concepts like strings or all the way up to the potential size of the universe. That's pretty big, and you have to scroll for a long, long, long time time to get back to human scale from there. It's kind of terrifying, honestly. Try not to think about it too much.
Goime 500, a platformer by Cary Huang, might look a heck of a lot like Achievement Unlocked. And, with its 500 achievements to earn for every tiny little action, it plays a lot like it too. Comparisons are, of course, inevitable, but its webtoy feel and whimsical humor certainly helps make up for its lack of premise-innovation.