/plug (but it is free and open source)
You can run this inside Docker containers with a few extra capabilities (allow tap, allow ioctls) which is probably similar to what you need for other in-container solutions. You can also run it on intranet servers, desktops, phones, etc., and connect everything to a common virtual backplane.
Edit: you can also bridge this to docker0 since it supports Ethernet bridging and run it on a Docker host. We're working on better/cleaner Docker integration but it's all do-able now. Just takes a bit of sysadmin know-how.