MapTool is a free VTT (might have been one of the first) that is
available under https://www.rptools.net/toolbox/maptool/

We were using MapTool for a game of Labyrinth Lord recently, and I was
thinking maybe my notes on that might be of interest to... someone I guess.

* MapTool worked great until it didn't. At the end we had some issues
when two of us got disconnected while the others still could see things
move around. I think I should have restarted the server in that case,
but as it was in the very end of the 2hour timeslot we just played out
the rest without it.

* MapTool now has a function (marked as experimental) that allows to
create a server and connect to it directly from other clients. No more
futzing around with port forwarding in this case. Unfortuantely maybe
not as stable as it could be (see above). Still, the lack of such a
function was one of the reasons I did not use the software before, as it
would have been too much work to get it running with my network setup.
Now that problem is gone, it literally has become a matter of creating a
server, having players connect (they are prompted for a PIN), and their
computers downloading the media files from my computer.

* Speaking of media files, MapTool allows to use media files from the
players computers to use in the game. Those are also added to the
campaign file automatically. In fact it even allows to run a remote
server where the campaign file is stored, I just haven't been able to
try that one yet. But other than that? Want to have a new token? Drop a
picture in the related TokenTool, make a suitable token, then just add
it in a folder and use it as you will. Nice.

* I do find the use of MapTool surprisingly convenient. There are a few
things that one can't do in the tool (e.g. animated maps would be nice,
but can't be done in the current architecture), and some stuff that can
be done but needs to be configured properly (noone has bothered to
create a script framework for OSR games yet it seems), but I have a lot
of options to show the players exactly what I want them to see. Still
there are a few things that I still have to figure out.

* The dynamic lighting in the dungeon is of course the star of the show.
One can add a vision blocking layer and have PCs walk through the
dungeon and have them see whatever it is that they have a) lit and b)
what they can see. This can make for some interesting tactical gaming
where some monster or character can see some things, but cannot see
others. I noticed that it also takes a lot of mental strain from me as a
DM as I don't need to track either light or walking order in this case.

* The other thing that helps a lot is the way one can organize a
scenario here. Players can generally see 3 layers on the screen: tokens,
objects, and background, and they can interact only with the first one.
Another hidden layer is present, but is only available to DMs. This is
useful, as it allows you to drop information (e.g. attached to a
numbered token) at the appropriate places, and just call it up by going
over it on the token layer. As it's hidden it is not actually visible
for players, and you can have your whole adventure in there, slowly
following along as the PCs explore. Incredibly useful.

* That said, there was an annoying issue with players movign tokens over
specific (invisible to them) GM tokens with information, and me not
being able to access them then. I think this might have a button that
allows DMs to get a hold of tokens under oters. but if it has I haven't
found it yet.

* Not every part of the lighting system is perfect though. I still can't
make head nor tails out of elevations and depressions. I don't quite
know what to think about them. They don't update in ways that I would
expect from either. I would for example depressions with a light source
inside expect to be lit inside, but they aren't. The lighting system
also takes a little to register someone has updated settings. More than
once we got stuck in a place with a newly lit lantern not lighting
anything because we didn't move.

* Doors are one of the things I will have to get into more. It is
possible to create movable doors, but how is still a bit of a mystery to
me.