Below please find my primary writing tools.
GNU Emacs, Org-mode, and various add-ons (cross platform, open formats, free)
Emacs is my main tool for writing. Org helps me structure it and do other things. I use aspell for spell checking.
DevonTHINK (MacOS, open formats, expensive)
When I want to save and organize references I find on-line I save them to PDFs in DT.
BeOrg (iOS/iPadOS/WatchOS, open formats, free + paid add-ons)
This is one of my mobile capture tools.
DevonTHINK To Go (iOS/iPadOS, open formats, free-ish)
This is my other mobile capture tool.
NextCloud (cross platform, open formats, free*)
I have an instance I pay for that is outside the normal cloud infrastructure. I also am standing up my own personal private instance.
Home Network Attached Storage (NAS) (cross platform, all formats, expensive)
I have a complicated NAS setup at home. It is there largely so I can keep local copies of media.
Physical books (analog, paper, varies)
I regularly make use of different dictionaries, references, and odd bits of books.
White boards (analog, ephemeral, varies)
I mind map and note take and do other things on white boards. I never seem to have enough.