schematic capture program

 Xschem is a schematic capture program, it allows creation of hierarchical
 representation of circuits with a top down approach. By focusing on
 interfaces, hierarchy and instance properties a complex system can be
 described in terms of simpler building blocks. A VHDL or 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 very good speed
 performance, even on very big circuits. The user interface is built with the
 Tcl-Tk toolkit, tcl is also the extension language used.