Play! is a relatively new PS2 emulator that has the goal of being portable across Windows, OSX, iOS, and Android platforms. It is primarily developed by a single developer, that developer being Jean-Philip Desjardins.
Play! is written in C/C++ and is designed to make use of instruction caching and a dynamic recompiler scheme to try and achieve better performance while emulating the PS2’s complicated CPU.
The project is designed as a way for Jean-Philip Desjardins to sharpen his own programming skills and for him to gain more experience in the computer engineering and software engineering fields. Which so far, is an excellent showcase as the emulator is slowly but surely showing some good progress. It currently can run a few games, which is a great achievement in itself, but it runs them with a lot of issues.
If the development is kept up, Play! should become a fantastic emulator with a few years of active development put into it.