7-Zip - file archiver with a high compression ratio
You can use 7-Zip on any computer, including a computer in a commercial organization. You don’t need to register or pay for 7-Zip.
Free open-source disk encryption software
Free open-source disk encryption software for Windows Vista/XP, Mac OS X, and Linux.
Encrypt in real time, even as you add files. A wizard assists in creation of virtual encrypted volume (you define the size).