We’re running out of GAUPS shields. I took advantage of this and I updated the design. It is now compatible with the Arduino R3 pinout: it takes power for the digital side from IOREF, not from the 5 V pin. For older Arduinos or shields, there are solder bridges on the back of the board to configure it for either 5 volts or 3.3 volts. The IOREF solder bridge (the default choice) is shorted by a cuttable trace.
The fourth driver can still be used as its own axis, or as a second driver on the Y axis. However, I have replaced the header and the two jumpers with solder bridges, pre-wired for dual-Y operation. To get a separate fourth axis, cut the DY traces and bridge the A pads.The savings from not including a header and a pair of jumpers that 95% of the users don’t need almost exactly offsets the cost of the R3 Arduino headers (four additional pins total).