The Electric VLSI Design System is an open-source Electronic Design Automation (EDA) system that can handle many forms of circuit design, including: Custom IC layout Schematic Capture (digital and analog) Textual Languages (such as VHDL and Verilog) ...and much more. Electric is free software, and is an official GNU package.
FidoCadJ is a very easy-to-use editor, with a large library of electrical symbols and footprints (through hole and SMD). Drawings can be exported in several graphic formats (PDF, EPS, PGF for LaTeX, SVG, PNG, and JPEG). Although very simple and not relying on any netlist concept, FidoCadJ uses a file format containing only UTF-8 text, very compact and suited for copying and pasting with newsgroups and forum messages. This determined its success, being apt for simple mechanical drawings as well a
The SimulAVR program is a simulator for the Atmel AVR family of microcontrollers (ATtiny and ATmega). SimulAVR can be used either standalone or as a remote target for avr-gdb. There are interfaces for Python and Tcl. When used in gdbserver mode, the simulator is used as a back-end so that avr-gdb can be used as a source level debugger for AVR programs.