Here are some resources for building your fabulous worlds, both in constructing things like maps and in developing a world that feels rich and real.
Don’t forget that building your world includes both the physical aspects of the world (where it is in its solar system, how much water compared to land, active plate tectonics, etc) as well as the cultures of the people who inhabit the world. Culture doesn’t form in a vacuum; it is influenced by the space, the weather, the circumstances.

Fractal World Generator square map output
Resources and Applications
Fractal World Generator
Includes fantasy, science fiction, weird fiction, and D&D filtered generators for names, calendars, worlds, demographics, adventures, and travel systems. The main page literally has a planet generator – enter percentages of water and ice, choose your output (you can have an animated globe if you like).
Open source. Free, but takes ko-fi donations.
Inkarnate
Online map-making tool for role playing and fantasy writers. Maps can be highly detailed with high quality art. Create maps for your world or region, cities or villages, battles, or scenes.
Includes both free and paid versions. If you want to publish your Inkarnate map(s) in your books, you do need to get a paid subscription (though you can use the map even after your subscription expires).

Inkwell Ideas
While many of Inkwell’s resources are geared for role playing, quite a few features will be of use to the speculative fiction writer. This includes a coat of arms design studio, a Java based app. Another is Cityographer, which lets you instantly create a city map and details (residents, store inventories & prices, etc.). You can have the program do it all at once, or run it in a step-by-step fashion, editing the map and details as you go. Everything created is always completely editable. There is also at least one good article on developing or creating religions for your world.
There is a free version and a paid version of Cityographer.

Map from Medieval Fantasy City Generator
Medieval Fantasy City Generator
This application generates a random medieval city layout based on a couple of criteria of a requested size. The generation method is rather arbitrary, the goal is to produce a nice looking map, not necessarily an accurate model of a city, and you can use the existing district labels or turn them off. With the warp feature, you can adjust your city’s district lines.
Mithril & Mages
This is a fantasy writer and role player’s playground that includes name generators for a variety of needs, utilities for role playing, and even a few generators using modern data (businesses, city blocks, college majors, criminal history, wound and disease prevalence) that may be useful in worldbuilding.
World Anvil
This is an online worldbuilding tool for authors. You can use it to create maps, timelines, characters, and species. The goal is to allow you to organize your world and search through everything and anything with ease. There are articles to help you through tough spots, and a global community of users you can engage with and get feedback from (you can also keep your stuff to yourself, if you prefer).
Free to use. Currently in beta.
Articles
7 Deadly Sins of Worldbuilding
Excellent article written by Charlie Jane Anders that hits seven of the worst things you can do (or forget to do) when creating your world.
Fantasy Worldbuilding Questions
Science Fiction Writers of America (SFWA) series of articles written by Patricia C. Wrede covering how to create a world that feels real. While not all sections apply to all stories, this is a good read for anyone new to world building or for whom this is a weakness.
How Fast Could you Travel Across the US in the 1800s?
This is a nice historical article with maps and details on the rate of travel across the US throughout the 1800s as various modes of transportation were developed.
Mythcreants
This is a blog full of fantastic articles on worldbuilding, inspiration, and storytelling, specifically for writers of science fiction and fantasy.
Other Writers Resources
Here are some links for blog posts on world building from other writers.
Worldbuilding Resources – Kathryn Sullivan
Check out my other research and resources for writers posts here.