The Open JTAG project has as objetive to give to the public domain a complete hardware and software JTAG project. Based on a simple hardware board, composed basically by a FT245 USB front end and an Altera EPM570 MAX II CPLD, this board is capable to output TCK signal at 24 MHZ using macro-instructions sent from the computer end.
It is not as others JTAG projects based on the PC parallel port: Open JTAG project uses the USB channel (still not at high speed) to communicate with the internal CPLD, sending macro-instruction as fastest as possible.
You can visit the official page of the project at http://www.openjtag.org