We've just released WebStone 2.5. Both executable and source code are available for free and will stay that way.
Tests are reproducible.
The previous version of WebStone used a time of day random seed. Now it can optionally use a fixed random seed. WebStone 2.5 comes with a new license designed to encourage you to contribute enhancements while protecting you and your company from liability. There is an optional new dynamic workload that simulates ad rotation. Future Enhancements Mindcraft wants to encourage the WebStone community to make enhancements for everyone to use.