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.
PolyNome - PolyNome is a comprehensive practice tool for musicians.
KanbanMail - A Kanban board for your emails.
Everypixel - Stock Image Search Engine That Filters Out Trash. Made for designers who hate bad stock images.
Sunsama - Calendar and scheduling for teams
Writty - An open-source text editor to help you focus on what matters