I read on Wikipedia that the original version had a multiplayer which is sadly not availlable in the re-release.
I thought that I tell you this because some people who played the original version back in the days, may expect a multiplayer and I can't find a clue on the gamesite if the game is singleplayer and/or multiplayer.

But it's a nice game anyway.

I've found info on Steam forum (it seems that developer is quite active there), that there is a possibility, that multiplayer will be added to "renewed" version of Vangers, but it's rather far perspective, since dev admitted, that they're for now focused on other suggestions of community. Sorry that I haven't provide a link, but I can't remind, in which thread dev mentioned about this thing.

Why doesn't this version have multiplayer?

See above, thanks for the necropost.

At this point, I'd be surprised if the devs are still working on Vangers.

What does it have to do with the devs, put out the version with multiplayer out like you did with alt versions of zak mckraken or broken sword

I know I'm digging an old thread - but for the good reason. I was incredibly surprised, but authors have restored multiplayer. Yes, it's available also in GOG version!

Although from what I've read on Steam forum, it may be a bit capricous in functionality. But it's there! A very positive surprise. And it seems that the update was there for some time, I didn't even notice it.