ReiserFS offers a revolutionary new approach to file system design.
It not only stores the file names. It stores the files themselves in a B*-tree.
The program is a generation ahead of the alternatives, which use older, plain, B-tree technology. However, ReiserFS cannot store the files themselves in the tree.
ReiserFS doesn't suffer from log congestion, either. You can use it to effectively create a 100,000-entry directory, and it is fairly unique in that respect.