A low-ish-level implementation of high-level language features like real-time variable viewing and modification, timing, program control (stepping et al.) and even arbitrary function calling with type checking. Works with C/C++ fairly generally (has worked with cl, tcc, gcc and g++ (mingw-w64) on windows so far using dlls; doesn't require compiler-specific debug information). Requires some integration, but this is considerably simplified so extraneous effort is minimized.
Currently it is past major development, unless magically good ideas are proposed/discovered and really should be implemented. It has now just become available as well (so be warned of beta software!).
The implementation languages are C/ASM (asm for function calling). It shall be under the MIT license upon release.