1. A method performed by a host computing device, the method comprising: receiving a request to execute an application on the host computing device, wherein the host computing device has a corresponding host instruction set architecture and the application comprises first application instructions from a guest instruction set architecture that is different than the host instruction set architecture; loading a processing unit emulator and a guest operating system together into a first process with the application, wherein: the processing unit emulator translates the first application instructions into second application instructions in the host instruction set architecture, and the guest operating system provides at least one guest operating system interface that is called by the application; and running the application by executing the second application instructions on the host computing device, wherein the first process comprises a shared address space that is shared by the application, the processing unit emulator, and the guest operating system, and wherein the host computing device comprises a host operating system that includes a second process.