If ever there was an app that was deceptively simple, Atomdroid is it. At first glance, it appears to be a fun, exploratory chemical drawing tool. Users can construct molecules one atom at a time from the periodic table, choosing the bonds and the atom positions as they go. (It is reminiscent of the chemical building kits from organic chemistry class.) However, this is just the very beginning of what Atomdroid can do. The app allows users to open pdb (or another format, xyz) files, and with those files, the app becomes a powerful computational resource. It performs Monte Carlo simulations and analysis, as well as local and global energetic optimizations. One downside to the app is that its features are not necessarily intuitive to use, and at present there do not seem to be any introductory materials available for the app.
Platform: Android phone
Cost: Free