MathIsFun Times Table - Learn Your Multiplication Tables
textadventures.co.uk - Create, play and share text adventure games.
GCompris - Educational Game for Children 2 to 10 years old.
Ink by Inkle - ink is a popular open source scripting language for branching stories, designed for writers
I Know It - "I Know It" is an online game for practicing primary-level math concepts.
Mudlet - Mudlet is a freshly-minted MUD client, designed to take mudding to a new level.