Twitter acquired the company that makes TextSecure, Whisper Systems, last month. In countries where governments have more strict control over wireless networks, Whisper Systems' apps have been extremely helpful to dissidents wanting to communicate and organize securely.
Now Twitter has just turned TextSecure into open-source software, meaning those same dissidents can engineer new features and adapt the software for their own purposes, potentially making them even more secure.
Whisper also has another app, RedPhone, which encrypts voice calls on Android devices, though that one hasn't been made open source yet. Twitter says it's going to open up Whisper's products slowly, saying in a blog post that it needs to "make sure it meets legal requirements and is consumable by the open source community."
Both TextSecure and RedPhone were unavailable when Mashable tried to download them from the Android Market earlier today. (See the clarification below.)
The apps certainly had their fans. Movements.org, a nonprofit dedicated to connecting "grassroots digital activists," cites Whisper Systems' apps in a how-to on securing Android devices. The company's transition to Twitter wasn't smooth for the users of its apps, though -- the company had to take RedPhone offline right when Egypt's elections were happening last month, leading to many complaints.