When my friend Brett Terpstra told me he released an app, my immediate response was, “I’m in.” Brett has brought us some amazing donation-ware, including my beloved NValt. To be honest, I’d buy Brett’s new app just on principle. Marked (App Store Link) opens Markdown, MultiMarkdown, text, and HTML files and previews them as HTML documents. It watches the source document for changes and live updates. This means you just got live Markdown preview for any text editor for just 3 bucks and you are helping out a swell guy while you are at it. Go get it.