Google Drive - Access and sync your files anywhere
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.
Dropbox - Online Sync and File Sharing
Notion - All-in-one workspace. One tool for your whole team. Write, plan, and get organized.
Box - Box offers secure content management and collaboration for individuals, teams and businesses, enabling secure file sharing and access to your files online.
Slack - A messaging app for teams who see through the Earth!