ChatScript runs fast and from my research it looks like it handles dialogue very well. On the other hand, it appears to have only a single active developer.
Rasa on the other hand, looks much more actively developed.
I guess I'd like to know the trade-off in terms of performance and complexity between the two.
I am the Product Manager at Rasa.
I have never heard of ChatScript, but it looks like it is written in C++. Rasa, on the other hand, is written in Python. However, I talk to developers constantly and have yet to see an AI assistant built with Rasa that was constrained by the performance.
The Rasa team and its thousands of community members are actively improving the open source framework and the tooling that layers on top of it every day. It's really easy to get started and there are tons of resources. From a quick check, it looks like the approach of learning from real conversations, ML-driven dialogue management engine, and focus on building a community are the main differentiators.
I recommended asking this question on the Rasa Forum too.