TrueCrypt was a virtual encrypted disk software package (freeware, source-available, but not technically considered "open source" because of its use of a nonstandard license) which was mysteriously discontinued in May 2014, leading to all sorts of theories about why this happened. Users were officially requested to switch to the Microsoft disk encryption utilities, but some have developed open-source forks of TrueCrypt instead.
The official TrueCrypt sites (truecrypt.org and truecrypt.sourceforge.net) have been pretty effectively purged of all tech docs, with even the Internet Archive copies disabled, illustrating how anybody wanting to be sure of maintaining access to some particular document ought to keep their own copy of it independently of all outside institutions which might abruptly pull it or be pressured into doing so by others wanting it to be pulled.
In keeping with the discontinuation, the latest official release only extracts and decrypts data that was encrypted with earlier TrueCrypt versions, but no longer supports encrypting any new data. Various unofficial sites archive earlier versions which encrypt and decrypt, and some sites are pursuing possible future development of forked versions.
Truecrypt supported a kind of steganography called "hidden volumes".
- Wikipedia article
- Official site
- SourceForge site
- Phase 1 Audit Security Assessment
- Mysterious announcement from Truecrypt declares the project insecure and dead
- TrueCrypt Final Release Repository (unofficial)
- Archive of TrueCrypt releases
- TrueCrypt revival site
- Source files relating to file format