ChemCrafter
Description:
This is an iPad app (only for iPad, I'm afraid!) sponsored by the Chemical Heritage Foundation.
What it does is to simulate an old-time chemistry set, with all the dangerous chemicals. You start with alkali metals in water, and work your way up to heating reactive metals in air with a blowtorch, and mixing alkalic metals with halogens. There's a strong emphasis on BOOM.
Unfortunately this is not suitable for classroom use, at least for me, because you can't get random access to particular reactions. But it is a lot of fun to play with, and perfectly suitable (recommended) for children.
The YouTube promotional video is below.