Zweifish is a tiny file encryption application using 256-bit Twofish encryption in CBC mode. Twofish is one of a few ciphers included in the OpenPGP standard. Requires Mac OS X 10.7 (Lion) or newer.
Download and test in trial mode: Zweifish Enterprise Edition 1.2
At present Apple's Sandbox keeps the Zweifish Home Edition from renaming files when files are accessed directly (i.e. when you choose files and not their containing directories). Version 1.2 addresses this issue, as far as yet possible, by using security scoped bookmarks: you only need to choose a directory once and Zweifish retains its access rights to this folder. Henceforth files within this folder can be accessed directly.