FreeOTFE is a discontinued open source computer program for on-the-fly disk encryption (OTFE).

[3] FreeOTFE was initially released by Sarah Dean in 2004, and was the first open source code disk encryption system that provided a modular architecture allowing 3rd parties to implement additional algorithms if needed.

The FreeOTFE license has not been approved by the Open Source Initiative and is not certified to be labeled with the open-source certification mark.

This allows it to be used under Microsoft Windows without installation of the complete program to "mount" and access the encrypted data through a virtual disk.

[12] Instead it lets files be stored and extracted from encrypted disk images, in a similar manner as ZIP and RAR archives, by using a Windows Explorer like interface.