BiModem was one of the last file transfer protocols developed for use in bulletin board systems.
Unlike the predominant protocols of the day (XMODEM, YMODEM, ZMODEM), BiModem allowed BBS users to upload and download files at the same time.
This resulted in significant time savings when a 1 megabyte file would take more than an hour to transfer, at 130 to 250 characters per second over a 1200 or 2400 bit/s modem.
It was released in the end of 1989, and before it saw widespread use, HS/Link was created which was easily added to BBSes and allowed for file lists and bidirectional transfers.
Part of the problem with BiModem is that very few sysops and users wanted to wade through the instructions.