Signal

Details

The project is provided under an AGPLv3 license. This is the license used for all their client sources.

The Android application does appear to require, and be built with, a range of non-FOSS libraries including Google Play Services. This has been queried by users on GitHub, with responses indicating little desire to produce fully FOSS app versions. There are some external FOSS focused forks like Signal-FOSS and Molly.

The application talks to a server, which is also provided under an AGPLv3 license, although a portion code related to spam handling is omitted from the provided FOSS codebase under the reasoning of security:

To keep Signal a free global communication service without spam, we must depart from our totally-open posture and develop one piece of the server in private: a system for detecting and disrupting spam campaigns.

While the server component does appear to be self-hostable, little official guidance & support is specifically provided for this use-case, with the project only advising assistance via their unofficial community forum.

The project had also previously failed to provide updates server sources for a almost a year.

While alternative clients and servers can be used, Signal is not designed to be federated, and the founder has indicated that they’d prefer forked application versions not use their naming or server resources.

The project is supported by the Signal Foundation, which received $50m in funding by one of the foundation founders. Signal has also received $3m in funding from the Open Technology Fund, which itself is primarily funded by the US government. The foundation and project also appear to gain funding from donations.