Roll20 - Roll20 is a suite of easy-to-use digital tools that expand pen-and-paper gameplay.
D&D Beyond - Official online toolset for Dungeons & Dragons tabletop gaming
Foundry Virtual Tabletop - A self-hosted, modern, and developer-friendly roleplaying platform.
MasterScreen - MasterScreen is the ultimate set of tools for running tabletop or online roleplay campaigns and managing intricate fictional worlds. Free for everyone.
Fantasy Grounds - Fantasy Grounds is a virtual tabletop to help facilitate play of tabletop-style role-playing games...
MapTool - MapTool is a 100% community driven and 100% free to use online, multiuser, networked, graphical, interactive, programmable virtual tabletop.