BiModem
BiModem was one of the last file transfer protocols developed for use in Bulletin Board Systems. It was created by Erik Labs, and was revolutionary for its day.
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 using 130 to 250 characters per second over a 1200 or 2400 bps modem. In addition, it had a chat feature. This would allow the user and the sysop to converse during the upload/download of files.
BiModem never received widespread acceptance. It had to be manually patched into both BBS and terminal emulator packages, and it was incompatible with some programs. It was released in the end of 1989, and before it saw widespread use, HSLINK was created which was easily added to BBSs and allowed for file lists and bidirectional transfers.
Part of the problem with BiModem is that very few SysOps wanted to wade through the instructions and the same with the Users. Sysops that successfully made a ZIP file with BiModem and a pre configured shareware copy of ProComm with the batch file to run BiModem. Adding this file available as a FREE download made this the second most used file transfer protocol on my BBS. Z-modem was far and above the most popular. We like some other boards had free users and paid users. Free users had an upload/download byte ratio to maintain and kept us in new files. Paid users would pay to not have to bother with upload/download byte ratios. This is what made BiModem popular with us and probably others.
The final version (BiModem 1.25) was released in 1991.
In 1995 a program was released in Argentina called BiModem Pro 4.0. This was a user modified version of BiModem 1.25 with some minor bugfixes.