BitVisor employs a parapass-through architecture. Most I/O accesses from the guest OS pass directly to hardware; only security-critical I/O is intercepted by the hypervisor. Because it reuses the guest OS’s own device drivers, no large emulation layer is needed.

Single-VM design keeps the codebase small and easy to understand. Widely used for hypervisor research and OS kernel education. Runs Windows and Linux transparently as the guest OS.

Source code is available under the 2-clause BSD license. Free to use, modify, and redistribute for any purpose, commercial or non-commercial. Download from SourceForge.