Subversion is a version control system that can be used for managing versions of files, such as programming source code, text documents, web sites, or image collections. Here are some links:
Here is my attempt at a MySQL file system backend for Subversion.
And here is something similar but less ambitious and more useful: a Subversion repository indexer.
Here are some things I'm looking forward to in Subversion, in no particular order. Many of them aren't priorities for the rest of the Subversion community, so I may end up attempting them myself.
svn obliterate command.