Information about calculators e.g. HP-48 is at HP-Calculator.Org, they are hosting the HP-48 FAQ. HP-48 Kermit Hints and Tips shows how to talk to the HP48 via its serial-line Kermit protocol. The HP-48 may also be used as a Linux terminal.
See also at my pages about Linux with Infrared Devices and Linux and Pocket Calculators .
GtkTiLink is a program which allows you to transfer data between a Texas Instruments calculator and a computer. It works with all cables (parallel, serial, Black and Gray TI Graph Link). It supports the TI82, TI89, TI92 and TI92+ calculators. It can send/receive data and backups, make a capture of the calculator screen and do remote control.