A Type Coupler: Toohey's, Coopers, XXXX, and most craft beer/microbrewery kegs.
D Type Coupler: Carlton Draught, CUB, Fosters & VB Kegs.
S Type Coupler: Asahi, Heineken, Hofbrau Kegs.
Home brew ball lock.
You can have as many taps as you like, limiting factor is the size of the fridge to cool...