Trello - Infinitely flexible. Incredibly easy to use. Great mobile apps. It's free. Trello keeps track of everything, from the big picture to the minute details.
Really Good Emails - A large collection of good product email design.
Taskade - Make lists, organize your thoughts, and be inspired to get things done. Taskade is a collaborative space for your tasks.
Good Sales Emails - Best sales emails from great companies
Perfect Wiki - Build and organize your knowledge base of company resources without switching between workspaces
Great Email Copy - A dose of emails from around the web.