One of its features is to provide a RESTful view of relational tables in a database, in a manner reminiscent of PostgREST. One difference is that with Denodo Express you must explicitly import tables from the "wrapped" database into the Denodo server that works as intermediary. The Denodo server can wrap other databases besides Postgres.
I wrote a bit about it here: http://productivedetour.blogspot.com.es/2014/12/connecting-t... (although I don't really cover the REST aspect.)
ZenQuery is similar in that it creates REST API endpoints for your database tables / specific SQL queries. However, it's database-agnostic and runs as an independent web application.
May I ask what your use case is?
The website http://www.sandman.io/ seems to be down - expired last November.