I use the free version of Evernote every single day. From to-do lists and research notes to writing entire chunks of articles, it's proven helpful at every step of the writing and editing process.
One great feature? Its mobile, desktop, and web apps sync automatically as long as you have an internet connection. (And if you work offline, it'll sync the next time you have internet.) Plus -- and this is super important for content creators like us -- it's constantly saving and syncing your work automatically, making it a safe place to write and store ideas.