An open source device to connect a computer with an RS232 serial port to a telnet BBS. It does not use an analog phone line but internet through a wifi connection. Behaves like a Hayes dial-up modem, and it is designed and built for old computers. Plug it in, fire up a terminal emulator, and use the Hayes AT command set to tell it what to do. Can theoretically be used with any computer that has an RS-232 port.

Occasionally the designer sells them on eBay, but you can build your own.