For mathematically inclined researchers (or students who wants a hands-on way to familiarize themselves with the Hodgkin-Huxley equation or Hidden Markov Models), XPP is a fantastic and free virtual playground! Incredibly vast in its computing capabilities, this app will solve differential equations, run simulations such as those mentioned above, solve boundary value problems, and more. The XPP app uses plain text files called ODE files, some examples of which are preloaded in the app, and thousands more of which are available from the internet or via iTunes import. Conveniently, the “help” section of the app is quite comprehensive and includes a section to familiarize users with the ODE syntax. Users can create and edit their own code within the app.