I found the Reactive Manifesto while researching executable specifications.
The key concepts:
- Responsive (ie fast handling of user input)
- Resilient (ie keep going in face of failure)
- Message based (everywhere)
- Elastc (responsive under varying workload - and predictively reactive rather than after the fact).
The find came from this paper on executable business processes which was interesting to me because it referred to BPMN.