World Anvil - World Anvil is a worldbuilding tool for Authors, Storytellers and worldbuilding lovers.
StoryMill - Developers and publishers of Mac, Win, and iOS productivity, home and office and writing software such as MacGourmet, Paperless and many more. Based in MN.
Kanka.io - Kanka.
Manuskript - Open-source tool for writers.
Notebook.ai - A smart notebook that grows and collaborates with you
Novelize - Novelize is an online novel writing app designed to keep authors on track.