bit banging
FTDI (a series of USB to serial converter chips also supporting a bit bang mode) 2MGUI (a DOS driver by Ciriaco García de Celis utilizing bit-banging to support non-standard ultra-high capacity floppy disk formats "bypassing" the normal floppy controller logic, a similar program for Amiga floppies is Vincent Joguin's Disk2FDI) Light pen (on MDA, HGC, CGA and EGA PC-compatible graphics cards the sensor of an optional light pen could be read in a fashion similar to bit banging) Virtual machine (VM) (implementing virtual device drivers emulating actual hardware controllers sometimes involves utilizing programming techniques similar to bit banging)