I am looking for an interactive exploratory tool to embed in a commercial application. I am looking for a commercial-friendly licensed open source alternative to the wonderful Tableau system
Take a look at Pentaho. It's built from open source parts so you should be able to reuse parts of that. There's also R, though that is really more of a statistical programming framework than an ready-to-use exploratory tool.
If you're looking for something that's as easy to use as Tableau though, I'm afraid you won't find any open source solutions.