Main domain told me almost nothing. The documentation link transforms it into what should've been their homepage given it's presented like a whole, different site with everything you need.

http://tachyon-project.org/documentation/

Never heard of it before. Seems... possibly useful if they would actually tell me what its useful for then perhaps I might find the documentation more engaging.

Anyone has experience with this project? We are currently thinking about using it in our cluster with Spark Streaming instead of an external DB (MongoDB)

we use it, but (after reading the homepage linked to at the bottom) pretty clearly outside the core use case. In particular, we use it for off-heap caching, which we configure through org.apache.spark.StorageLevel. We monitor via tachyoneFolderName which as you probably know is a spark context (sc) attribute (eg, ./bin/spark-shell, then type "sc."[Tab] to find it).

Url changed from https://github.com/amplab/tachyon, which points to this, which seems like a better starting place.