Thanks utpalme for the heads up !
It's not actually a tracker, if I'm not mistaken, but It does hold an impressive selection of books.
Plenty of free goodies + ridiculous cheap ones (I just paid 0,01 $ for one I'm pretty sure I won't find on any e-learning tracker)
Most of the times I used scribd for my academic needs, but I'm positive I'll use this one as well in the future.