The source code for the existing Silent Text version is here and the company tells me that the new Silent Text source code will be released sometime in March or April after confirming legal issues such as licenses for third-party libraries.

FORBES: Pressure Increases On Silent Circle To Release Application Source Code

When Netscape released the source code of its web browser in March 1998, it wanted to involve other companies.

ECONOMIST: Computer programming

Kerberos gained pre-eminence because it is clever, and because its developers, computer scientists at the Massachusetts Institute of Technology, released the source code, which let security experts around the world debug and refine the program line by line.

ECONOMIST: Microsoft

While some of the deployed protocols are in the public domain, the source code for particular applications have not been released yet making it difficult for security researchers to render an informed opinion on its implementation.

FORBES: Pressure Increases On Silent Circle To Release Application Source Code

The Oculus folks -- no longer a single man, but now a company of around 20 employees -- worked with Epic Games on getting the source code up and running for the hardware prototype, though it's unclear if it'll ever actually be released to developers or the general public.

ENGADGET: Hands-on with the newer, larger Oculus Rift prototype (video)