There was a version of KA9Q NOS with multitasking that could serve telnet, ftp, smtp, bbs, convers, and more plus give you multiple switchable terminals for telnet, ftp, all at the same time on an 8088 and connect to a packet driver for modem, ethernet, or AX25. It was a port of BSD networking with its own multitasking capability.
Also PC/MIX was pretty cool.