Owlbear Rodeo is described as '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'. There are nine games similar to Owlbear Rodeo for a variety of platforms, including Online / Web-based, Windows, Linux, iPad and Mac. The best alternative is Roll20, which is free. Other Owlbear Rodeo like games are Foundry Virtual Tabletop (Paid), MapTool (Free, Open Source), Fantasy Grounds (Paid) and Astral Tabletop (Freemium).
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!
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.
MapTool is an 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.
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.
Battlegrounds: RPG Edition (aka BRPG) is virtual tabletop software designed to enhance your pen-and-paper roleplaying games, whether your players are in the same room, or on the other side of the world.