Windows: Finding a good text editor can be tough. Some lack basic features, like spell checking, and others are so heavy they may as well be word processors. Write! is a new application, currently in beta, that rides the sweet spot and delivers the features you'd actually find useful without the cruft (or system bloat) you don't want.
Write is gorgeous, and has an interface that fits right in with Windows 10 (or Windows 8 for that matter.) You get your choice of interface: a tabbed interface for multiple documents (although you can ever only see one at a time), a simple, borderless window for distraction-free writing and note taking, or a heavier Word-like UI that includes menus and toolbars.
Write! also includes automatic spell-checking, a dark mode and a light mode so suit your preferences, tunable autocomplete that can learn to finish your words for you, tons of keyboard shortcuts and key commands to save you time, support for Markdown, Wiki, and Textile syntax, and productivity counters for things like pages, word count, and more than you can set as goals.
The app also auto-saves your work all the time, so you don't have to worry about doing it yourself. If you sign up for an account (which you'll have to do to download the app) Write! will also automatically save your folders and documents online for you too, so you can get at them from any other computer. You also get unlimited undo, so pressing Ctrl+Z even after closing and opening a document -- or even moving to another computer -- actually undoes the last action in the doc. You can also organise your documents into writing "sessions," which are, like session-saving in Chrome or Firefox, available to open, close, and re-open on other computers.
Write! is Windows-only, right now, with OS X and Linux versions of the app on the way. Some of the banner features (like cloud saving and unlimited undo) are free for "early adopters," (aka everyone who signs up right now) while everything else will be free forever. The service plans to introduce "Pro" accounts in the future that make use of some of those connected features.