(Check back in as I add details on how I use each, the features I like, and how I integrate everything together into dashboards for myself and clients)
Project Management (planning & estimation)
Arbor makes creating backlog, organizing projects and themes, and estimating really easy. Arbor allows for simple integration between slack and trello (see below for more info on them) which makes it easy to collaborate.
Trello is quick and simple kanban task management. With the ability to create custom states it makes it easy to provide detailed status reports.