Gerbv is an open source Gerber file (RS-274X only) viewer. Gerbv lets you load several files on top of each other, do measurements on the displayed image, etc. Besides viewing Gerbers, you may also view Excellon drill files as well as pick-place file
Ngspice project aims to improve the spice3f5 circuit simulator.
Icarus Verilog is an open source Verilog compiler that supports the IEEE-1364 Verilog HDL including IEEE1364-2005 plus extensions.
QSapecNG is a Qt-based symbolic analysis program for linear analog circuits. In fact, it consists of two indipendently parts: the SapecNG framework engine, and the application gui QSapecNG.
A GTK+/Gnome2 graphical front end for the IW3HEV Vector Network Analyzer, also has a signal generator, and It displays graphicaly SWR, Phase, Return Loss, X impedance, Serial resistance, |Z| Impedanze, and Inductance, and capacitance.
"mprfgen" is a multi-port memory generator that can be used for VHDL designs. It can generate either generic or Xilinx-specific (through component instantiation) multi-port memories.