- Drag-and-drop what-you-see-is-what-you-get UI instead of script-based. Smooths out the learning curve.
- Supports putting state displays in the middle of the circuit, so you can directly view normally-inaccessible information instead of inferring it from experience or algebra.
- Fast. It updates all displays interactively, as you edit the circuit. Very easy to experiment, e.g. just drag a gate around seeing what it does in different places.
This isn't quite a simulator, but a co-operative board game to understand quantum computing (featured on HN a few weeks back): https://entanglion.github.io/
It doesn't take much (LOC) to implement a simulator. You can understand how one works by reading the source: https://github.com/adamisntdead/QuSimPy