Project shyknight is a classic-style platforms game like Manic Miner and some others from early 80s. It has very nice and polished, colorful retro graphics, and simple but addictive gameplay. Eric is in love with a greedy girl named Martina. He must collect all the items she wants to make her happy.
Zyan Drench is a simple yet very entertaining game developed using the Zyan Communication Framework. The Game board is a random picture of size 15x15. Start from the top-left corner of the board. Select a new color for the top-left pixel, and all adjacent pixels of the same color will be painted over with the new color. The goal is to drench the whole board with your own color. Zyan Drench has several modes: play against Android phone (with adjustable skill level), play solo (classic single-player mode), and network game. It is completely ad-free and open source.
QMentat helps you practice mental arithmetic. It uses arbitrary-length fixed point arithmetic, and can handle any size numbers, only limited by the size of your screen (and in the case of division with an integer result, the speed at which the number can be factored). It is also quite configurable, allowing you to tailor the questions to your needs.
Galois is a computer game of the "falling blocks" type, but with unique features. Unlike most other games of that type, it is not limited to blocks made of four two-dimensional, square bricks: you can choose among several different brick shapes, blocks composed of more or fewer bricks, and even between two- and three-dimensional games.