When I started writing, I tried using MS Word and Google Docs but after ten thousand words, both became unwieldy. I have Scrivener, but I didn't have it installed everywhere, and it wouldn't install on a Chromebook, so it too wasn't quite what I needed. So, I built my own.
I can write my stories, novels, and anything else I need to write, keep track of characters, add notes, and collect things in series. Importing from the PublishersArchive database, it also can keep track of potential markets and submissions. An API lets me share my progress on my blog effortlessly, and a collaboration tool lets me share my manuscripts with proofreaders and editors, who can print it or download it as an RTF or EPUB if they prefer.