Popularity of the mode might see an increase come the New Madrid letting loose. It's fun to play with legacy stuff however. Also for hf use there is some bbs for 300Bd mode, but most packet is of the psk variety these days;
The manual for rpr has a good technical description of the mode;

WinRPR: Saving Robust Packet from oblivion • Virginia Packet Network
The creator of Robust Packet has graciously ported a form of TNC code to Windows making Robust Packet available as a sound card mode.
vapn.org
The manual for rpr has a good technical description of the mode;