MapTool is described as 'online, multiuser, networked, graphical, interactive, programmable virtual tabletop. Requires Java 6+. It can be used for face-to-face play, or Internet role-playing in real time even if your players are on the other side of the world' and is a virtual tabletop. There are more than 10 alternatives to MapTool for a variety of platforms, including Online / Web-based, Windows, Linux, Mac and Steam. The best alternative is Roll20, which is free. Other great apps like MapTool are Inkarnate, Foundry Virtual Tabletop, Owlbear Rodeo and Fantasy Grounds.
Roll20 is the free, easy way to play tabletop games (such as pen and paper RPGs) online with others. It's completely web-based, so it runs right in your browser. It supports video and voice chat, background music, character sheets, a massive art library, and more!
Inkarnate is an all-in-one fantasy mapmaking platform with a free version and a huge library of assets. With Inkarnate, one can create world and region maps, city and village maps, battlemaps and interiors, as well as scenery maps.
Foundry VTT is a standalone application built for experiencing multiplayer tabletop RPGs using a feature-rich and modern self-hosted application where your players connect directly through the browser.
Owlbear Rodeo is a simple VTT that requires no registration and offers map sharing and drawing, dice rolling, voice chat, and other features that allow for a simple-to-use tabletop encounter experience.
Standard Action is a tabletop gaming application designed to be simple, but flexible. In game, Standard Action features an interactive game board, live chat, dice rolls, a turn tracker, customizable token stat bars, and much more.
Beyond Tabletop is a set of tools for RPG players with easy-to-use online character sheets and maps. Subscription-free and designed to be used on all devices online. Currently offering a battle map and character sheets for Pathfinder and D&D 5e.