RCL, a simulator for Texas Instrument calculators from the 70's.
...go to http://www.rskey.org/CMS/index.php/the-library/12 (The site owner does a great job at preserving the history and the documentation of calculators of the period.)
RCL is targetting developers interested in applying the Von Neumann architecture and attributed grammars and developers with a need to do complex calculations in their applciacation.
SharpPath is a C# implementation of the PATH language. Its main focus is to provide an easy way to write and debug PATH scripts, as well as eventually extending the language to make more complex applications possible.