I mostly use TrueCrypt for cross-platform directory encryption. With all the uncertainty about its future, I started thinking about how to replace it with a more trusted encryption utility. GPG works well for individual files (in Emacs, encryption and decryption occur transparently), but not for directories. I decided to try using the common filesystem mount-unmount model and adapting it to GPG-encrypted tar files. The resulting prototype zsh code is in the linked gist. Seems to work for me, and has enough error checking to avoid clobbering data (but I'm sure it still has bugs).