Desqview was acceptable to run a two-line Dial-up BBS on the same machine. It had stability issues beyond that so when the need arose for a third line we moved to OS/2 which was wonderful to multitask DOS applications in. The internet killed our little BBS before we had a need for four lines and beyond :)
There was a cottage industry of software to get around DOS' single-tasking limitations. DoubleDOS was another program that let you have multiple sessions. There were terminate and stay resident (TSR) program like Sidekick.
