Dominions 5 is a very complex game and assistance can be very helpful. To this end Dominions players have created a plethora of helpful tools, references, and programs.
The Inspector (link) by Larz is without exaggeration the single most important tool in the dominions community. This is true to the newest noob, the oldest vet, the casual player, the modder, everyone. It has the stats of every unit, spell, item, site, and event all taken straight from the source code. It is almost perfectly accurate (map moves and gold costs on mounted units can be a bit off) and kept up to date. It even has every single sprite in the game available for download for modders.
Illwinter's documentation page has a set of manuals to go along with the game, a game manual, a map making manual, a modding manual, and a technical manual. These manuals provided by Illwinter and a few old vets are mostly accurate and reasonably well updated but have been known to contain some outdated or wrong information. They should be used but not relied upon.
Will show remaining pretender points with all available pretender chassises for a given build (nation - paths - scales - awake/dormant/imprisoned status). Available at Pretenders Calculator, was not updated recently, so does not include Ind, Na'Ba and the new Middle Eastern pretender
Calculation tool for many odds you may care about. From hitting those horrible elves to how much fatigue a spell is going to cause in your communion. Has not been updated recently, and could be using Dominions 4 numbers, but a valuable tool nonetheless. Available at https://dedas.github.io/dom4calc/#meleetohit.
Lets be honest with ourselves, Illwinter's map generator for Dominions sucks. The maps are ugly, often produce small cap circles, and province borders and connections can be a bit wonky. Some players don't mind but most do. Being the productive bunch which they are they Dominions community has made some efforts to solve these problems, both through handcrafted maps, and more pertinently to this page, random map generators.
MapNuke, formerly Automated Improved Dominions Starts, is a procedural map generator made by nüke. MapNuke is currently the most popular random map generator for Dominions with most long form games using it. It is FOSS and available for download on Itch.io with a link to the GitHub there as well.
Cartographic Revision (also known as CR) is a slightly older map maker for Dominions, and while it has been eclipsed by MapNuke it is none the less well loved. Currently CR is missing the newest nations as it has not been updated for a few months. It is available for download on Itch.io.
This is really good for maps made with the in game generator, or any time you want to set nostarts on a map en masse because they don't have enough connections. Dominions 5 Random Map Nostart setter
These tools are designed to do a single thing and do it well.