The lander demo is also know as the game Zarch (or Virus for other computers). David Braben (of the Elite[1] fame) wrote that in three months[2] for the release of the Archimedes.
Zarch, now available for your web browser: http://news.ycombinator.com/item?id=4052784
These machines had BASIC in ROM, and you could write WIMP programs with it. Lots of fun.