Dragon Ball GT: Revised is a fanfiction by Kaboom, dedicated to taking materials from Dragon Ball GT, but crafting them to be much more enjoyable and accurate to the source material than the show itself ever was. To quote another friend of mine, 'GT is full of great ideas, it just had horrible execution', and that's what this story strives to fix.
The story starts out mostly the same, with lots of familiar events still in place such as Goku being wished into the body of a child, his going into space with Trunks and Pan, and the search for the Black Star Dragon Balls – but there are lots of changes both major and minor to make the series much more enjoyable, such as a more satisfactory origin for the Black Star balls to begin with.
In addition to the main story, Kaboom occasionally draws and posts new artwork based on and/or inspired by his fan-fiction, character bios, downloadable copies of the story, and other such things to add to the story. There's also a side story, 'Cataclysm', which details the new origin of the Black Star Dragon Balls, with some interesting past characters being involved.
The story is still ongoing at a very irregular pace, but each addition is well worth the wait when it finally comes. You can read the main story here, while 'Cataclysm' can be read here. For even more GT Revised goodness, you can follow along with Kaboom's updates over in it's official-unofficial thread on Kanzenshuu forums. Be sure to leave a good review of the fic if you enjoy it!