Mac only: If you're a big fan of apps like WriteRoom or TextWrangler, free utility Quickcursor will let you use them for more projects by instantly moving text from your current application to your favourite text editor.
QuickCursor sits in your menu bar and waits for you to activate it by clicking on its icon, which produces a drop-down menu displaying a list of compatible text editors. By clicking on one of them, QuickCursor will automatically paste the currently active text in your frontmost window into that editor. When you finish writing and you leave that editor, your edited text will automatically be pasted back in the original program. Thus, if you're writing an email in Mail.app, writing a blog post in Safari, or working on a document in Pages, you can seamlessly move to your favourite editor to do so and back again with little effort.
The biggest downside to QuickCursor is that it doesn't currently work with every application (notable exceptions include Chrome, Firefox and Microsoft Word). However, in certain situations this isn't a huge hassle — if you know you want to work on an email draft in WriteRoom, you can always just open up Gmail in Safari and let QuickCursor do the rest. The app is open source, though, and the author is currently working on expanding compatibility, so we hope that we'll see our favourite browsers working with it in the future.
QuickCursor is a free download, Mac only.