Originally Posted by
acitrano
Surprised no one has mentioned
Jetico's BestCrypt. I know it's not open source (although they do publish their encryption and keygen routines), but their volume and container encryption is excellent, fast, and secure.
The linux version (at least) of BestCrypt is open source. It and TrueCrypt are (were) very similar.
To the OP: I could suggest separating the problems of encrypting flies on disk v. being shared. For things on local disk, use some combination of full disk encryption + BestCrypt or some other "container" encryption.
For encrypting individual files (e.g. to share), there are countless tools. One answer might be GnuPG in symmetric mode:
gpg --output doc.gpg --symmetric doc