If you're looking for actively developed cross platform free software alternative: http://www.getsafe.org/
It is not full disk encryption, so not a direct alternative for a product like TrueCrypt. I believe it uses a RAM disk for the files so you're limited in size, too - something like that.
Personally I'm not a big fan of using WebDAV to expose the encrypted file system - it seems like a large liability. But I'm not a real security expert at all, just saying it sounds complicated to get right (caching could keep a unencrypted copy) and exposes an even larger attack surface.