Homebrew sniffing Bluetooth at the air interface level is notoriously difficult.
In 2013, I added Bluetooth Low Energy support to gr-bluetooth. The project is based on software-defined radio techniques with GNUradio, and I used the USRP to capture RF traffic.
The USRP is relatively expensive, however, the ubertooth is an open and inexpensive Bluetooth experimenter's platform by the same nice folks who started gr-bluetooth.
The OpenOCD project provides low-level debugger access to several CPU/MCU cores and SoC's. I have contribued to the flash support for TI's TMS470 and Freescale's Kinetis MCUs.
In 2011, I cloned a Konami Arcade Machine in VHDL, and used it to play an 80's fave, Time Pilot. If you're interested in getting the code, let me know and I'll post it.
Coreboot is open firmware capable of replacing the stock BIOS on some Intel-based computers. In 2008 I published this recipe to get a pared-down version of gPXE running on coreboot.