TL;DR
Aalto University has introduced an open-source project called the Lighthouse Stylus, a six-degree-of-freedom (6-DoF) spatial stylus designed for projection-based interfaces. This device aims to provide an affordable alternative to costly motion capture systems, achieving better than 1 mm positional accuracy for around $155 in parts. It utilizes Valve's Lighthouse tracking technology through the Tundra Tracker ecosystem, but while the stylus's design and software are open source, it still relies on proprietary components for tracking.