The DM Toolbox is a collection of digital and physical tools I personally use as a Dungeon Master, creator, or player. Some are free, some have free editions, and others cost money. I in no way profit from sharing these tools and am not sponsored by any of the creators. Many other options exist, but these are the ones I chose to use and standby from hands-on experience.
FoundryVTT is, personally, a dream come true. It is a feature-rich and system agnostic virtual tabletop with all the bells and whistles. Intuitive to use with a clean UI. Manage the game with compendiums of creatures and items, build sessions and take notes with journals, quickly setup a scene with a map, lighting, walls, and token vision. Build upon core functionality with user made modules and custom macros.
Dungeondraft is the battle map counterpart to Wonderdraft. It speeds up map making with easy to use terrain painting, adaptable floor plans, smart tiling, and object scattering. With a built in lighting system it's possible to create beautiful and moody scenes. The floor plan tool makes ship building a breeze. Dungeondraft now supports importing custom asset packs, giving the user endless possibilities. It can be finicky at times, but is worth the patience.
Dungeon Painter Studio (DPS) is a tool for building encounter maps. This is what I primarily use to build maps, pre-Dungeondraft. It features custom grid settings, object effects, paintable terrain textures, wall tools, and robust export options. The default selection of assets packaged with the software is slim, but the Steam Workshop community provides a variety of packs to easily install and it's simple to add your own.
FREE | $25/yr
Inkarnate is a web-based map making application that's free to use with paid pro features. While encounter maps can be made with Inkarnate, it was built with world and region maps in mind. It's easy to get started with and the free options are generous. I created my first ever map using the free assets two years ago. Since then Inkarnate has significantly increased it's production quality. With enough creativity the provided assets can be used to create stunning pieces of art well outside the intended use case.
TokenTool 2.1 is straightforward software that makes creating consistent looking tokens quick and easy without opening an image editor. Drag in the file you want, adjust zoom, pick an overlay frame, and export it. It comes loaded with a selection of frames and supports adding your own. From the creators of MapTool.
MapTool is a bit of misnomer, as it is fully capable virtual tabletop that you can also, if you're patient, build maps in. MapTool is completely free with the option to make a donation. It receives semi-regular updates and just recently implemented support for importing Dungeondraft maps. Host a game, track initiative, create macros, setup maps, tokens, character sheets, and chat with players. The UI is dated and intimidating, but it's a worthy VTT and chock full of premium features like lighting, vision, and fog of war.