R

reimplementation

An open-source GoldSrc engine clone (Clean authentic reimplementation without using reverse-engineered code)

A reimplementation of BioWare's Aurora engine (and derivatives). Pre-pre-alpha :P

https://xoreos.org/

A simple printf implementation in C89

Dark Game Kit is a cross-platform reimplementation of DarkGDK and DarkBASIC Professional (IDE and compiler) written in C++