The facets let you support counting and group by - is there something else you had in mind?

Edit: You can get a pretty quick idea of what's supported the query language at http://senseidb.github.com/sensei/bql.html. Since Sensei was designed with document and text uses cases in mind, we have plans to support advanced queries where a relevance model is part of the query, allowing you to perform a custom sort on the server.

sum() and distinct() come to mind for sure, but I don't know how easy they'd be to implement. The particular use case I have in mind is where we have events streaming in and we usually don't care about the actual events, just various sums, counts and distinct counts over them grouped by various dimensions.

Database-side aggregation is something in the works. We are incorporating a patch as we speak. We find more and more in house projects using Sensei as a BI tool, we see this functionality more and more important, so stay tuned :)

Would you guys be interested in collaborating on that? At Mozilla, we've been using ElasticSearch in a few places as a NoSQL style BI tool. I read through the SenseiDB docs and can see many places it could be almost as good of a fit as ES, and with a little work, I bet it could be just the thing.

Absolutely!