Dangerous Prototypes recently announced the availability of the open source Bus Blaster v2 in their shop (here the announcement).
The Bus Blaster is an USB tool to debug microcontrollers and embedded cores in general, and its design is completely open source. I already did a post on the first version of the Bus Blaster, but version 2 is much better. The selling point of this board is that it substitutes many other debuggers by emulating different protocols with the configurable CPLD and FT2232H on board. It can support JTAG, SWD, and could also support other debugging interfaces that does not exist yet. It can be used with many debugging tools such as OpenOCD, urJTAG and others, and with all this functionality it costs very little (around 35$ now).
In particular, the possibility of using the ARM Serial Wire Debug is a nice addition; some microcontrollers based on Cortex-M (like the Stellaris and the STM32) have this interface because it occupies only two pins, against the 4-5 pins of the JTAG interface. Having a microcontroller with low pin count eases the design of the PCB and the circuits around, and potentially enables smaller products.