I haven't used this, but I know of it: I believe that that the idea is to provide the simplest, easiest abstraction over PostgreSQL (and only PostgreSQL). Rails does run-time introspection, and it doesn't cost much.

Massive.js is written by Rob Conary, and is descended from his .NET projects Massive and SubSonic. There was a time when SubSonic was arguably the best light-weight ORM for .NET: if I ever meet him, I owe him a beer for making SubSonic.