Call me parochial, but until a few minutes ago, I'd never heard of MFC/R2, and certainly had no inkling it might be important. Apparently:
MFC/R2 is a telephony signaling protocol, which dates back over 50 years. Its full name is the Multifrequency Compelled R2 Signaling System. It was originally used to provide register to register (i.e. switch to switch) signaling over analogue copper pair wiring at a higher speed than had been possible with pulse dialing. It was widely used for international circuits, and many national ones. Later, with the advent of E1 PCM trunks, MFC/R2 was adapted for use over this new medium. Though seemingly a relic from the past at a time when SS7 and ISDN are widely deployed, digital MFC/R2 over E1 trunks is still heavily used in many countries.
The reason I needed to know this factette was because of an absolutely classic free software story from Digium, the company behind Asterisk, the leading open source product in the super-hot category of software-implemented telephony:
At Digium, we’ve even contemplated licensing a commercial MFC/R2 stack and making it available to our users, just so that Asterisk can be easily used in as many places and applications as people want to use it. However, earlier this year, a young man in Mexico decided he had enough of this situation, and that he was going to write an MFC/R2 stack from scratch, integrate it into Asterisk, and provide the result back to the Asterisk community. He met with Mark Spencer at an event, chatted with him, got Mark excited about the project, and Mark came back to Huntsville fired up enough to write some additional code in Asterisk and Zaptel that was needed for this new stack to do its work. That man’s name is Moises Silva (moy, in the Asterisk development community) and his project has taken on a life of its own now. He has his OpenR2 stack working with all major versions of open-source Asterisk, and it is being used in countries around the world, and gaining support for additional countries as developers in those countries find out about it and add the needed enhancements for their country’s particular flavor of R2.
It's the classic hacker question, which has produced so much great code – and will keep on producing great code: just how hard can it be for me to add feature X? And it's a question that can only be asked of free software.