Rainglow Color Themes - 320+ color themes for a variety of editors and software.
Really Good Emails - A large collection of good product email design.
Slack Themes - Make your Slack pretty with custom themes
Good Sales Emails - Best sales emails from great companies
eM Client - eM Client is a fully-featured email client for Windows and macOS with a clean and easy-to-use interface. eM Client also offers features for calendars, tasks, contacts, notes, and chat.
Great Email Copy - A dose of emails from around the web.