Discourse is an open source Internet forum software application founded in 2013 by Jeff Atwood, Robin Ward, and Sam Saffron. Our client asked us to develop several plugins to let users embed Google Calendars and Google Spreadsheets in a post, add any HTML snippet as a sidebar and export user statistics. This last one was merged into the Discourse core.
We proposed to them a series of developments for a very specific niche, requiring R&D over new technologies, and they have successfully done it. I think they are ideal for disruptive projects, research and quick production delivery.