It occured to me that I've been suggesting apps I don't really use.

When dealing with forum forms, I shamelessly use my trusted partner, Notepad++. Plaintext is best text, no argument. When I need decent spellchecking I chuck the entire thing to MS Word and let it do its magic. When I'm doing actual writing it's either FocusWriter (immersive writing a.k.a oh god did i just write down 5k words in an hour) or MS Word (proofreading, editing, anything else), using a file format that can be opened with both (.odt). Not really a fan of online text editors because the folder that contains most of my writing is backed up online already.

There are also applications/web apps I found immensely useful that's not a text editor. TheSage is an offline dictionary and thesaurus that would've been the best thing since sliced bread, if not for its donators-only update cycle. Seventh Sanctum is a random content generator where I have stolen countless names from. Lastly, Evernote, for when that flash of inspiration occurs when I'm not anywhere near a computer.