TCL, The Common Link, was a Swedish BBS system developed by Ulf Hedlund in the late 1980s. It was based on the capabilities of the KOM conferencing system used at many Swedish universities, and distinguished itself from the other major FidoNet BBS systems at the time by its support for topic threading and its non-hierarchical command interface. It used a Btrieve database for information storage. There were only about 30 TCL BBSs in Sweden and only one outside the country.
References
The Common Link Wikipedia(Text) CC BY-SA