SHaT
Layer 2 Address Translation Gateway
"Source Hardware address Translation" provides an Ethernet to IP gateway. Ideally, any Ethernet network client can communicate through the gateway with the IP world on the other side regardless of what the client network stack is configured as.
See the project website for how it works.
The project has been dormant since 2006 but I would spend some efforts to round and hone edges if there is public interest.