This is one I spotted on Steam today, the Roll20 and Fantasy Grounds alternative GM Forge is on sale today - and it has a couple pretty good reviews. This is a good link as well in the discussion forum on the differences between this and other software:
What I like about this one is if the GM owns the software players can join your game for free, without owning the software. No subscriptions either, and your content is stored on your machine. The software also supports Steam Workshop content, so there is the possibility of new games and adventures being modded in and packaged up for download. There is also talk of a stand-alone server coming soon, so you will be able to run this on another machine and log in to manage the game.
Cons?There are a couple complaints about the UI and also a learning curve, and I have got in and messed around and I can confirm that. It does feel (at the moment) just a little bit on the beta/early side of polish but I am sure that will get better as time goes on. The app also maximized on my large monitor and it was a huge space to manage, so I am hoping for a windowed mode (or a way to resize the app). It doesn't feel slick, but it does the job.
There are also some users making note of having to port-forward and expose IPs, but I am sure someone will write a FAQ on how to sort all that out and use a VPN service if you don't want your IP out there. Then again if you are running Internet/open games like that those are issues you should probably be thinking about all this before you start a game. Maybe someone (or the developer) will create a matchmaking service and we won't need to worry about this, so you never know.
This is also Windows only software at the moment on the GM side, but players can join anywhere they have a browser.