When I was at OOW this year I saw the new (?) Oracle Live SQL web environment in action during the Oracle JSON Hands-on Lab workshops. I had a go at it and I liked it very much. As far as I know they will/might introduce it on the internet as well for, for example, Oracle By Example (OBE) environments and test it yourself courses / workshops.
To give you the scoop, here are some screen shots. Hope you like them as much as I do (like the KISS look-and-feel).