HTML && CSS
- Foundation. Responsive front-end framework.
- Bootstrap. Another front-end framework but with a really nice collection of JS UI elements.
- Emmet. Powerful HTML/CSS shorthand plugin for your text edtor.
- ISO-8859-1. HTML entities reference.
Markup || Down
- TextMate 2. My go-to text editor. Maybe I'm just nostalgic.
- Sublime Text. Another text editor, I like it, but more than TextMate?
- Sequel Pro. Powerful MySQL management tool for people who like a GUI.
- Virtual Box. Free virtualization for all platforms. Great for testing emails in Outlok 2007 and websites in IE if you're on a Mac.
- Ink. Responive email framework from ZURB.
- Premailer. Takes a normal HTML file with styles in head, media queries, etc and makes it all inline.
- The Ultimate Guide to CSS. List of supported CSS tags for most email clients.