DM Helpmate is described as 'offline, downloadable DM (Dungeon Master) companion for Windows featuring an interactive database, links to spells and spell slots, attack and damage dice rolls, skill checks, filtering by parameters and tags and much more'. There are more than 10 alternatives to DM Helpmate for a variety of platforms, including Windows, Online / Web-based, Mac, Android and iPhone. The best alternative is Roll20, which is free. Other great apps like DM Helpmate are D&D Beyond (Freemium), Fantasy Grounds (Paid), Astral Tabletop (Freemium) and Adventurer's Codex (Free, Open Source).
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!
A fun, easy to use, Open Source tool for tabletop RPG players to manage their characters, campaigns, and parties. The goal is to help you focus more on the game by bringing your paper character sheets into the 21st century.
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.
Rolisteam helps you to manage tabletop role playing games with remote friends/players. It provides many features to share maps, pictures and it also includes tool to communicate with your friends/players.
PlanarAlly is a web tool that adds virtual battlemaps with various extras to your D&D toolbox. Self hosting, Offline support, Simple layers, Infinite canvas, Dynamic lighting, Player vision, Initiative tracker. Free to use and is open source.