Free world-coupling software?

[egfdevos]

"I do not need it. Just want to know if simple FREE versions exists."

Why?
The cost of an IP-Interface vs IP-Router.
Lets say one uses 2 IP-Routers. That's about 2x €250,- = €500,-
2 IP-Interfaces and a Raspberry PI is about 2x €150,- + €50,- = €350,-

Useful options:
uni/bi directional routing. (Isolation. For maybe a multi home building/Hotel?)
Rerouting GA (For connecting two completely different KNX installations.)

[meti]

Considering a multi-home building or hotel project these additional 150€ in a multi million Euro budget are probably well spent.

For private projects or tinkering there is Calimero, knxd and you can probably build such thing with xknx.