Ballplay Genius is an easy to understand puzzle game, but with challenging puzzles. You can play puzzles in random order so no problem if you can't solve one. And due to the puzzle editor more puzzles can easily come.
Picture Puzzle Game
Imagine is a simple picture puzzle engine that allows you to puzzle with basically any picture (supported formats BMP, JPEG and PNG). Due to the underlying JCR5 engine (http://jcr5.sourceforge.net), it's easy to make bundles of pictures to swap with friends or over the internet. (Please respect people's copyrights when you do so!!!) Imagine has a simple language engine implemented and comes initially in both English and Dutch, but translations in more languages (maybe yours) are possible.
War In Space (AATM) is a classic space shooting game, with a LUA underground. For the less technical people, it's just a fun space shooting game that starts very extremely easy but will get harder as the game progresses. Fun for hours.