"Gdrive" (here: http://pramode.net/articles/lfy/fuse/pramode.html ) and the "Gmail Filesystem"/"GmailFS" (here: https://web.archive.org/web/20060424165737/http://richard.jo... as mentioned elsewhere in this thread) were both built on top of `libgmail` (here: http://libgmail.sourceforge.net/ ) a Python library I developed.
There were a couple of different projects at the time (listed in "Other Resources" on the project page) that sought to provide a programmatic Gmail interface.
I still have a "ftp" label in Gmail (checks notes 15 years later...) from the experimental FTP server I implemented as a libgmail example. :D
The libgmail project was probably the first project of mine which attracted significant attention including others basing their projects on it along with mentions in magazines and books which was pretty cool.
I think my favourite memory from the project was when Jon Udell wrote in a InfoWorld column ( http://jonudell.net/udell/2006-02-07-gathering-and-exchangin... ) that he considered libgmail "a third-party Gmail API that's so nicely done I consider it a work of art." It's a quality I continue to strive for in APIs/libraries I design these days. :)
(Heh, I'd forgotten he also said "I think Gmail should hire the libgmail team, make libgmail an officially supported API"--as the entirety of the "team" I appreciated the endorsement. :) )
The library saw sufficient use that it was also my first experience of trying to plot a path for maintainership transition in a Free/Libre/Open Source licensed project. I tried to strike a balance between a sense of responsibility to existing people using the project and trusting potential new maintainers enough to pass the project on to them. Looking back I felt I could've done a better job of the latter but, you know, learning experiences. :)
My experiences related to AJAX reverse engineering of Gmail (which was probably the first high profile AJAX-powered site) later led to reverse engineering of Google Maps when it was released and creating an unofficial Google Maps API before the official API was released: http://libgmail.sourceforge.net/googlemaps.html
But that's a whole other story... :)