PC-BASIC is an interpreter for GW-BASIC files. It can run and convert between ASCII, bytecode, and "protected" (encrypted) .BAS files. It implements floating-point arithmetic in the Microsoft Binary Format (MBF) and can therefore read and write binary data files created by GW-BASIC.
HGL is a compiler/interpreter suite for developing images. It features its own simple but powerful language, Lua integration, output in various formats as well as runtime input handled by plugins, and easy integration into various environments like Web servers or graphical applications. The input is taken from a source file, which has to be compiled for quick and frequent access by the interpreter. An interpreter then runs the compiled files, takes input from custom plugins (if neccessary), and outputs its result via custom plugins.
UnQLite is a in-process software library which implements a self-contained, serverless, zero-configuration, transactional NoSQL database engine.It is a document store database similar to MongoDB, Redis, CouchDB, etc. as well a standard key/value store similar to BerkeleyDB, LevelDB, etc. It reads and writes directly to ordinary disk files. A complete database with multiple collections is contained in a single disk file. The database file format is cross-platform, and you can freely copy a database between 32-bit and 64-bit systems or between big-endian and little-endian architectures.
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.
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.