The "Open On-Chip Debugger" provides JTAG/SWD access from GDB (or directly with TCL scripts) to processors with ARM and MIPS based cores.
See website for full list of supported targets.
Integrated Development Environment for some microcontrollers based on 8051(e.g. AT89S8253). Supported languages are Assembly and C. It has its own simulator, assembler, editor and many other tools. See the project web site for more details and the newest updates.