The informix port is slow and no longer being extended because the author feels their support is inadiquate. Depends on the used engine. Yes its possible to connect to any mentioned database anywhere in the net.
Replication is planned.
Onyx is a 4gl based on the idea of model view controller. Onyx 4gl connects to a transaction manager based on a OO-Parser generator via a socket. While the design goal of the protocol was to keep it as simple as posible, its a good starting point of writing vendor independent database applications.