ring3k is a user mode kernel capable of running Windows 2000 and XP compatible native applications on a Linux platform. It is a light-weight virtualization of Windows 2000 for the Linux x86 platform achieved by reimplementing kernel mode code as a ring 3 process in C++.

Vx32 is a user-mode library that can be linked into arbitrary applications that wish to create secure, isolated execution environments in which to run untrusted extensions or plug-ins implemented as native x86 code.