I found that, on a LAN, KEXI, running on one machine, can create a MySQL project hosted on another machine.

I would do the same trough internet with the second machine hosting on a separate LAN.

Does anybody have experience about ?

Database servers are addressed using the IP system or domain names. So any networks where you have access via the TCP/IP shall work. This is a property of database servers not how Kexi works -- Kexi adapts itself.

PS: And it does not matter what OS (Unix/Linux/Mac/Windows) is used for the server.

PS2: Bonus, encrypted (ssh) tunnels work too, just you need to set them up according to you operating system specifics; then it will be completely transparent to Kexi; you'd just connect to localhost (not local socket) and specify port of your tunnel. This is independent of database assuming you have ssh access to the server and ability to perform local connections from the server's shell account. Maybe in the future Kexi could set up a tunnel for you if you ask to with a mouse click or two.

(I hope I explained it in a form that would be useful for someone)