Microsoft To-Do - Task management tool
Sortd - Rated the #1 App for Gmail
Gone - An ephemeral to-do list
KanbanMail - A Kanban board for your emails.
KosmoTime - The to do list with super powers
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.