Virtual Tabletops
Industry giant. It's been around a while, and has lots of supported RPGs.
2D, top down, browser-based. Free, with premium paid features.
Has licensed official WotC adventure modules.
Integrate D&D Beyond with Roll20 and Discord using Beyond20.
"The Roll20 killer you should be using" - Cyanomys
2D, top down, browser-based. Free, with paid premium features.
Recently partnered with DriveThruRPG to allow users to import all of their purchased content.
Smooth, intuitive interface. Lots of useful features.
Heavy community involvement, with frequent updates.
2D, top down, browser-based. Free.
Smooth, intuitive interface. Get playing in minutes.
Still in development.
2D, top-down, browser-based. Free.
Includes a handy campaign journal feature.
Beautiful, snappy, intuitive interface, with pop-out window capability.
"A dream for power users, developers, and hackers" - Cyanomys
2D, top down. $50 for Game Master, who must host the server application. Free for players, who connect via browser.
Highly customizable, thorough feature set.
"For l33t gamers and automation enthusiasts" - Cyanomys
2D, top down, software. Game Master must purchase, then host. Players connect via client for free.
Steep learning curve, but very customizable.
Has licensed official WotC adventure modules.
3D. VR-compatible. Purchase and run from Steam. $10 on sale, normally $20. All players must purchase.
Import 3D models
3D. Beautiful lighting settings and asset collections.
Primarily a map maker, but other people can connect to play. Supports 3D dice rolling, and chat can be done through Steam overlay.
Honorable Mentions
VTT resources
ArkenForge - Make maps for Virtual Tabletops, or run it on a TV for use as a dynamic grid map with fog of war