taiHEN is a CFW framework for PS Vita™. When loaded with a kernel exploit, it acts as a common substrate for patching the system. taiHEN provides three main facilities:
It disables code signature checks to allow unsigned executables.
It exposes kernel peek/poke syscalls to user applications and allows loading of kernel modules.
Most importantly, it provides an API for hooking and replacing functions based off of substitute.
The last point means that developers can add custom patches to kernel, system applications, and games alike.