FoundryVTT

Newbie in the game of VTT’s but one of the best so far with over 600 systems, modules and add ons for gaming

Roll20

Probably the biggest online VTT out there.  2D, top down, browser-based. Free, with premium paid features. Has licensed official WotC adventure modules

Fantasy Grounds

Players connect via client for free.
2D, top down, software. Game Master must purchase, then host. 
Has licensed official WotC adventure modules.

Tabletop Simulator

Purchase and run from Steam. 
Import 3D models