This is astronomical simulation software which seems to be something like Celestia but a lot prettier - I'm not sure I understand its controls yet, but it looks like it could be pretty good if I spend a few hours with the manual etc. There doesn't appear to be a tutorial mode, which is a shame, unless I've missed something. Warning, file size is over 800mb.
Windows only so far, but they're working on Mac and Linux versions, and I'm told it will run under the WINE emulator.
http://en.spaceengine.org/
