There are 3 repositories under rebol-extension topic.
Rebol extension to SQLite (an embedded SQL database engine)
Access to GPIO and other IO functions on the Broadcom BCM 2835 chip, as used in the RaspberryPi
WebDriver client for the Rebol programming language. Can be used to automate browser sessions.
Blend2D extension for Rebol3 (drawing dialect)
Rebol extension for a Delaunay triangulation.
Rebol extension for Mathematical Expression Parser And JIT Compiler