So does anyone know if the GOG version of Trine 1 co-op includes LAN options? I read some Frozenbyte developers comments about them adding LAN options with their DRM free release and just wondering if this every actually happened as not finding much information on it elsewhere.

As far as I can see in the game, the only co-op is local with controllers.

[Edit]
Confirmed by one of the developers here: http://steamcommunity.com/app/35700/discussions/0/648814844045735846/

Which is ridiculous, considering online co-op was a major selling point of the new Enchanted Edition upgrade (and was included in the Steam version). Seems GOG users got the short end of the stick.

You should be aware that the post you're quoting and the post in the link are from before the Enchanted Edition update. The GOG version should have online co-op now, but I haven't personally checked myself.

If you check the store page for Trine Enchanted Edition, the following is written at the bottom:
Multiplayer notice: Trine supports mutliplayer via hotseat. Online or LAN play are not available.

When I click 'host a public/private game' it will try and then says: "Hosting Online Game Failed".

That's a shame as I bought a copy for my friend to play together. We live quite some distance away.

Maybe this is something that will be remedied once GOG Galaxy is released?

Just for the record, I have the Enchanted Edition and I can confirm that Quick Match mode is working fine, I tried it last night. However, there weren't any Public matches at the time, so I couldn't try that out. Additionally, I don't have a friend who owns this game in order to be able to try making a Private game so that we could play together online.

If I get a chance to, I will post it here.

The original Trine 1 was only done by plugging in two mice and two keyboards into your computer. It was tricky but worked well for me once I got it set up right.

Then they released Trine 2 that supported multiplayer, it was popular enough and people asked enough that finally they released Trine 1 using the Trine 2 engine. That is Trine Enhanced Edition.

It runs slower, but is supposed to support co-op over network.

@Sentaria:
That sounds like it might be a router issue to me. Routers try to block incoming connections to protect your computer. To fix that I keep hearing words like VPN, Port Forwarding, and Hamachi. I usually decide it's not worth when I start hearing those words, but hope you can figure it out!

Over the last few days I've played Trine 2 with a friend over a private hosted online game. It has worked very well. I've not tried the same with Trine 1 yet, but the menu look identical, so I assume that will work too. He has the steam version, but it still worked. Just make sure the firewall doesn't block things, as that was initially a problem when we set it up.

Playing like this was great fun btw, and being able to help each other out over tricky terrain is excellent. For example, the wizard holds up a plank, and the other person jumps on it and over some nasty traps. Then switch around characters (this works because we are only 2, with obviously 3 available characters).