Those two guys, Deadcode and CyberShadow, continue their work on the game. Considering the updates get distributed through Steam now as well, I suppose that makes them as official as they've ever been, although they were always hosted on the Team17 website anyway.
The CD and Steam versions of the game are compatible with each other in almost every way, including online, but each has its own very minor advantages and disadvantages. The Steam version has for example had some objectionable soundbanks and flags removed from it (easily downloaded and added back in by the user), but is kept up to date automatically via the Steam client. You probably got your copy from a Humble Bundle, by the way.