Educational Software for Ages 6-12 on Unix?

MarkB asks "I have an autistic five year old boy who is mad keen on maths, music and drawing. His school want him to have his own computer. I would like to start him on UNIX (rather than MS which the school offers) but need to find educational software suitable for young children. What software is available or being developed for the six to twelve age group? I am happy to join a project and get my hands dirty (java)."