WebDAV client libraries need pipelining support -- key for adequate performance. Also note pipelining is hard to add as an afterthought because it usually means library interfaces must be rethought to be event driven to handle multiple simultaneous requests waiting for responses.
Python 2.0 WebDAV library doesn't support SSL or Digest, binding, versions or ACL, but does support basics of RFC2518
Twisted could be a bit heavy if only the client functions of certain of its protocols are needed
C libraries for WebDAV support: Neon (doesn't do pipelining)
Look at CURL too, which does support pipelining. It does a number of protocols.
WebDAV servers: DAVServer was never really finished
Can use mod_dav and Apache -- plug our repository into pluggable store interface
There's a Apache POP3 module too
Apache is the ultimate extensible cross-platform open-source network server
Subversion built on Apache 2.0 successfully
Would need to turn Apache off for users who don't share -- requires reloading a config via sending a signal