TkGate is a event driven digital circuit simulator with a tcl/tk-based graphical editor. TkGate supports a wide range of primitive circuit elements as well as user-defined modules for hierarchical design.
upf2cpf is a cool command line tool which will takes in a UPF(Unified Power Format) and will convert it to a CPF(Common Power Format).This tool is very useful for Chip Design Engineers, who want to feed the power related info about the RTL in UPF/CPF.
esweep is a scriptable audio measurement program which features various signals and signal processing functions. Its main purpose is the measurement of speakers.
tkCybernetics is a small grafical tool for rapidly setting up simulations of simple cybernetic systems. It was designed for didactic purpose but might be useful for the quick test of some circuit too.