Schematic circuit editor for VLSI and Mixed mode circuit simulation.
Xschem is a schematic capture program, it allows to create a hierarchical representation of circuits with a top down approach . By focusing on interconnections, hierarchy and properties a complex system (IC) can be described in terms of simpler building blocks. A VHDL, Verilog or Spice netlist can be generated from the drawn schematic, allowing the simulation of the circuit. Key feature of the program is its drawing engine written in C and using directly the Xlib drawing primitives; this gives top speed performance, even on very big circuits. I have succesfully managed to simulate complete VLSI projects with this tool, both digital (Verilog / VHDL) and analog (Spice). The user interface is built with the Tcl-Tk toolkit, tcl is also the extension language used to send commands to the program. Schematics can be printed in SVG, PNG, PDF, formats. XSCHEM runs on Linux or other Unix-likes with Xorg server and on Windows with the Cygwin layer and required tools installed.
ChemVisio is software which might be useful for educational purposes (non-organic chemistry, crystallography etc.). It might be a good visualization support for all people who need better illustrations than that you could see in books.