What are some alternatives?
When comparing Roll20 and MapTool, you can also consider the following products
Fantasy Grounds - Fantasy Grounds is a virtual tabletop to help facilitate play of tabletop-style role-playing games...
Beyond Tabletop - Beyond Tabletop is a set of tools for RPG players with easy-to-use online character sheets and maps.
GM Forge - GM Forge is a Standalone Virtual Tabletop and is a sandbox for GMs.
Rolisteam - Rolisteam helps you to manage tabletop role playing games with remote friends/players.
Astral Tabletop - Create, host, and manage your tabletop role-playing games — online or in person
Dungeon Painter - Dungeon Painter is a free powerful encounter map design tool.