Update with a TLDR: I'm looking for an open source router appliance to make it EASY to control network / tunnel into VPN between a computer and a wifi/Ethernet network. Any proposed software solution is not good enough, there is a need to have a second hardware to prevent data leak even if the computer has its own VPN.

----

Is anyone aware of an open source project to create a gateway between 2 networks and force traffic over a VPN?

Basically, I think of a raspberry pi that would connect over WiFi and provide network to a computer on ethernet. The pi would establish a VPN and make sure the computer packets do not leak. This could also act as a simple firewall so that you can let the computer handle the VPN but to a couple of IP only.

I already designed all features that could be provided, how to manage the thing too, but before going further I wondered if such project did not exist yet? I wasn't able to find anything except expensive commercial products. And having to do all the configuration from something bare is not an option (due to skill issues for end users and risks of misconfiguration).