The FrontDoor system contained a Mailer, an Editor, a Terminal, a serial port device driver and configuration utilities.
[1] The task of mailers, the main task of the first FrontDoor release, was to accept a phone call for a BBS / FidoNet node system; differentiating between human and machine calls (sending the humans to the BBS while handling all other cases) and if the other end supported the same protocol started a conversation about handling whatever packets had to be exchanged, and calling external programs to handle the traffic.
[1] Joaquim Homrighausen attempted a "revival" of sorts of the project in 2014, but was prevented from continuing due to rehab from an injury.
In December of 2024, Joaquim Homrighausen managed to find all the required source code and tools to re-build FrontDoor once again.
FrontDoor runs under DOS and OS/2 as well as under most DOS-based multi-tasking environment (like Windows, DESQview, DoubleDOS, and more).