This app was mentioned in 7 comments, with an average of 1.00 upvote
A game called Sherlock from Everett Kaser Software. It's an ancient game from the long-ago year of 1991. But I love it, it's still fun, and you could run it on a potato.
Sherlock is a game about finding where goes where. Terrible explanation, but if you've ever done those "Sam is to the right of Sara" kind of problems in school, this game is basically that. I suggest getting Ultra but Pro is good enough. Free doesn't have nearly enough levels.
Sifar is pretty much dead but has enough levels to last you. It's a number puzzle game, no math involved.
Multitasking is a nice app for floating windows. It has a browser, notepad, calculator and other stuff. Pro version is like 4$. Don't remember much about the free version.
none* is a word based puzzle game. You are shown something and you have to guess what it is. Not much to explain here really.
QuizUp is fairly known but it's still great. Nice 1v1 quiz game. So many categories, from kid shows to sciences.
App of the Day is a good way to getting the full versions of free apps (Usually the IAP kind of freemium). Apps are hit or miss but you might get something nice there.
Playboard is like a feed of apps. People create their lists and publish apps they like.