AVaRICE is a program which interfaces the GNU Debugger GDB with the AVR JTAG ICE available from Atmel.
In recent times, GCC added support for the AVR series of microcontrollers.
This has been quite the boon for those of us who write embedded applications for processors with 'leaner' architectures.
Recently, Atmel announced the availability of a JTAG box for the AVR. Until now, there was no way to interface to this device with GDB.