TrueCrypt

Truecrypt is depracated. Veracrypt has inherited the code, added new functionality and improved security. Don't use Truecrypt, use Veracrypt; it's still open source, free and every bit as useful.

Truecrypt did pass a security audit, but since then vulnerabilities have been found. VeraCrypt, which also open source, has taken on the TrueCrypt code and improved it, including in terms of security. VeraCrypt is backwards compatible with TrueCrypt containers. You should use VeraCrypt from now on, and convert your containers to the VeraCrypt format.

[No.][non-cc]

TrueCrypt has not been approved under the [Open Source Initiative][1]. This is due to not following [The Open Source Definition][2] for software.

It is also using a custom licence which has been vetted and mandated as non open-source.

• [Fedora: Forbidden Items - TrueCrypt][3]

The TrueCrypt software is under a poor license, which is not only non-free, but has the potential to be actively dangerous to end users or distributors who agree to it, opening them to possible legal action even if they abide by all of the licensing terms, depending on the intent of the upstream copyright holder.

This is why TrueCrypt does not have the status: "Open Source".
(N.B. Wikipedia's status on TrueCrypt is just ["source-available"][4])

[1]: https://en.wikipedia.org/wiki/Open_Source_Initiative
[2]: http://opensource.org/docs/osd
[3]: https://fedoraproject.org/wiki/ForbiddenItems#TrueCrypt
[4]: https://en.wikipedia.org/wiki/TrueCrypt#ref_a
[non-cc]: https://en.wikipedia.org/wiki/TrueCrypt#Licensing_and_Open_Source_status "Wikipedia: "TrueCrypt - Licensing and Open Source status""

Free, but...
When one mean's "free" as in:

• "Free at point of downloading": Yes

• ["Libre software definition"][1]: No
  Be advised that according to the Fedora Project's "[Forbidden Items][2]" page:

The TrueCrypt software is under a poor license, which is not only non-free, but has the potential to be actively dangerous to end users or distributors who agree to it, opening them to possible legal action even if they abide by all of the licensing terms, depending on the intent of the upstream copyright holder.

This is indeed true as it states in the [licence][lic] (Section VI.2):

YOU MAY NOT USE, MODIFY, COPY, CREATE DERIVATIVE WORKS OF, (RE)DISTRIBUTE, OR SUBLICENSE THIS PRODUCT, OR PORTION(S) THEREOF, EXCEPT AS EXPRESSLY PROVIDED IN THIS LICENSE (EVEN IF APPLICABLE LAW GIVES YOU MORE RIGHTS). ANY ATTEMPT (EVEN IF PERMITTED BY APPLICABLE LAW) OTHERWISE TO USE, MODIFY, COPY, CREATE DERIVATIVE WORKS OF, (RE)DISTRIBUTE, OR SUBLICENSE THIS PRODUCT, OR PORTION(S) THEREOF, AUTOMATICALLY AND IMMEDIATELY TERMINATES YOUR RIGHTS UNDER THIS LICENSE AND CAN CONSTITUTE COPYRIGHT INFRINGEMENT (WHICH MAY BE PROSECUTED).

A more detailed breakdown summation of the licence can be found here: [FreeDesktop.org - TrueCrypt licensing concern.][3]

[1]: https://en.wikipedia.org/wiki/Free_software "Wikipedia: "Free software""
[2]: https://fedoraproject.org/wiki/ForbiddenItems#TrueCrypt
[3]: http://lists.freedesktop.org/archives/distributions/2008-October/000276.html
[lic]: http://www.truecrypt.org/legal/license "TrueCrypt License Version 3.0"

This is the best encryption software I've ever seen, out of a dozen of encryption software I've tried. Finding this application was a real stroke of luck (Thanks to alternativeTo). With a novice-friendly interface and explanatory wizard it provides a great way to encrypt existing partitions/drives and to create new encrypted file containers. A TrueCrypt file container can function as an ordinary volume by mounting it as a virtual disk and the concept of hidden volumes takes data security to a whole new level. On-the-fly encryption provides access to the data while keeping it encrypted at the physical level. If there were a rating system here, I would give it 5 out of 5.