Microsoft OneNote - While there are certain features you can pay to unlock, OneNote is a free software that is well regarded in the D&D community. You can break up different bits of information into multiple notebooks that also can be broken down into sections. You can use it by downloading the actual software or just using it in a web browser. It has most of the same tools that most word processors use.
Obsidian - Is very similar to OneNote in functionality. However, it can lend more to someone that wants to make graphs or visual idea boards. Note that you will have to download software to use it. It is free unless you are wanting to use it for commercial use.
Google Drive - If you are more comfortable with Google applications, Google Drive can be a great tool to store multiple files and keep yourself just as organized as other software will.
D&D Beyond Encounter Builder - This is a feature that allows you to build encounters by selecting enemies, placing them on a map, and planning out their power level by your party's average level. However, unless you are paying for a subscription, the amount of encounters you can have at one time is limited.
DND 5th Edition WikiDot - WikiDot is a source for both officially licensed content and popular homebrew content for DMs and players. The information within this source is mainly about the different types of characters that can be made, the features those characters can have, and the items those characters can have. It can be useful for creating NPCs, enemies, or player characters.
D&D Beyond Monster Manual - Is a resource if you are specifically looking for information on the various monsters in D&D
D&D Beyond Character Creator - This will walk you through each step and generate a searchable, editable character sheet that can also be exported as a PDF. Note that some character options and features are locked behind purchasing source books. However, it can be a great way to build the foundation for a character while using other sources to find other features, feats, and traits.
Hero Forge - A free-to-use website to create your own miniature figures for D&D. Note that it will cost if you want to purchase the files to 3D print them.
Inkarnate - This is a source that has both a free version and a subscription version. The free version is rather expansive. The paid version does unlock some asset packs to use in your maps. However, there is substantial positive feedback for the version. There is no download required.
DungeonScrawl - Another source with a free and paid version. The free version is quite expansive in terms of the maps you can make, and it does not require an account to be made. However, important quality of life features like auto-saving work, dark mode, and PDF export capabilities are locked behind the paid version.
DungeonFog - Yet another source with both a free and paid version. This site does require an account to be paid. However, the free version offers a wide array of map options, assets, and quality of life features like PDF and other file export capabilities, a user interface with not a lot of bright or intense light, and the ability to make your own hot keys for your map editing process.
