Reiserfs
 

Can someone explain to me what this file system is, and what are its advantages and disadvantages over ext3?

Second question would be that.. what other file systems are there? There are ext2, ext3 and reiser, but are there any more? (swap excluded) If so, are they more usable than ext3/reiser? Are the other file systems suitable for linux?

What is a filesystem: http://en.wikipedia.org/wiki/File_system

Comparison: http://www.debian-administration.org/articles/388