The JTAG adapter from 100ask.org is a USB-JTAG adapter, available e.g. on eBay. Although on the website the adapter is called „OpenJTAG“, I will only refer to it as 100ask-JTAG adapter, because it is not open hardware and especially not to be confused with the official adapter from the OpenJTAG project. OpenJTAG.org’s adapter is more sophisticated and upgradeable, as it is based on a Lattice MachXO2 FPGA, while 100ask’s only uses an FTDI FT2232D USB-serial converter to emulate JTAG, similar to Esden’s FLOSS-JTAG (and apparently many other JTAG adapters). According to the datasheet, the FT2232D has a maximum bitrate of 3Mbps.
Thankfully, upon request, I got the adapter’s schematics alongside permission to publish them to the public domain. With them I should quickly be able to present a working configuration.