Topicbox - Put team emails into one centralized, searchable place
Taskade - Make lists, organize your thoughts, and be inspired to get things done. Taskade is a collaborative space for your tasks.
InboxSDK - First usable API to write Gmail Apps for 1B active users
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.
Front - multi-channel inbox service for collaborative teams
Dropbox Paper Mobile - Organize your team’s knowledge in a single place