Mac: Last year, XKCD's Randall Monroe released Simple Writer, a web app that restricted your writing to the top 1000 most commons words in the English language. If web apps aren't your thing, Cleartext is a free Mac app that does the same thing. Cleartext follows the same principle as Simple Writer: when you're trying to explain something complicated, you want to use common language so more people will understand it. When you're writing (sadly, Cleartext doesn't support pasting text in), Cleartext highlights any word that isn't in the top 1000 most commonly used words to help you simplify what you're trying to say. This can be useful when you're preparing a presentation for someone outside your field, a big inter-office memo or if you're working on any other block of text that you're struggling to make readable. If you work in an industry with a lot of jargon, it can be helpful to highlight that jargon so you can come up with words everyone understands. As an app, Cleartext is a simple text editor, but it does support different fonts and text sizes alongside a full-screen mode. Cleartext isn't a tool you'll use all the time, but it's useful to keep around nonetheless.
Cleartext (Free) [GitHub]