This program's name or link were tossed around before on HLP, but I never saw anyone connect it with Freespace's Multiplayer, which is in dire need of a go-between (read: lobby) since PXO died.
The program basically makes your computer think that it's on a LAN connection with everyone that's populating the same room.
I use it to play Company of Heroes with my friends, because we can't choose the "Internet" option in the game, for reasons that are so obvious you really don't know anything about internet and games if you can't see them.
Now, Hamachi seems to mask (or convert or whatever-the-hell) your IP, and provide a "safe trusted zone", but you can also turn off the "trusting" components of it, because I wouldn't trust any of you with a pencil, ever, and if you're smart, you're just like me. The real deal here is that it will group people and give them a chat function, but it will also illuminate them in a way that a LAN network does, which would hopefully make Freespace games visible to and for people who are populating the same channel.
So essentially, you run Hamachi, join a Freespace "Network" with people in it (A network that is officially sponsored here and isn't managed by some dick), then you launch Freespace, choose the "LAN" (or IPX or whatever) option in the Multiplayer Options and see what games are going on the LAN.
At any rate, that's how Company of Heroes works, and I assume any other game would work in the exact same manner, it's just that I can't test it, because I don't care.
However if you care, then this potentially solves all the issues of PXO missing outright. If it doesn't work directly as I described it, then maybe some tweaks can be made somewhere (I don't know, I'm not a technically disposed person), be it to Freespaces MP config files or the Hamachi itself and then it would work.
Food for thought if anything. Just thought I'd throw it out there.