It's an Open Source project published under the GNU license. You can use the FREE version and if you like it you can get an extended version with some other features. Offering a basic compiler to convert Stamp II programs directly to PIC with little or no modifications. The compiler translates the SIL program into PIC16C84 assembly language. Command line interface, very powerful trace facilities.
All source code is available.
Here is the source code for both the assembler and simulator. Jeff Frohwein Loren Blaney's SxSim, a screen-oriented simulator. UMPS simulates a microcontroller with its external environment. Jeff Frohwein Designed for the Xilinx 4005 by Ernesto Romani.