Webots
Open-source robotics simulator with strong multi-robot and educational adoption. Alternative to Gazebo Harmonic. Generally faster cold-start, with a different physics engine and asset library.
Why It Matters
Different sim engines suit different problems; Roboticks supports both because customers actually use both. Switching engines per project is a config flag, not a rewrite.
How Roboticks Implements It
Same hosted-runner mechanics as Gazebo Harmonic. @requires_sim("webots") routes to a Webots runner. Self-hosted runners declare which engines they have installed via capability heartbeats.