seaLISP is a Lisp interpreter with as many bells and whistles as possible but with absolutely no dependencies apart from the C++ standard library. The garbage collector, the computer algebra library, and all other components are written from scratch to be portable. It also has a PSP port with some primitives for graphics.
NARS2000 is an experimental APL interpreter. The first NARS (Nested Arrays Research System) was designed and implemented in the early 1980s as a testbed for new ideas in APL, principally with nested arrays. A quarter of a century later, it's time to try again. The goal of this effort, as with the last one, is to foster new ideas about the language and its implementation. Language ideas include new functions, operators, and datatypes. Implementation ideas include algorithms to enhance code space (smaller executable), time space (faster execution times), or expressibility (clearer and more understandable code). A goal of the existing implementation is to be open and easy for others to change so new ideas may be inserted smoothly.