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.
Intercom - Intercom is a customer relationship management and messaging tool for web businesses. Build relationships with users to create loyal customers.
Notion - All-in-one workspace. One tool for your whole team. Write, plan, and get organized.
Plato - Share knowledge with your team through simple Q&A
Slack - A messaging app for teams who see through the Earth!
SavvyCal - A scheduling tool both the sender and the recipient will love.