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.
GoodGantt - The best Gantt chart for Trello®
Microsoft Planner - Microsoft Planner lets you easily bring together teams, tasks, documents, and conversations for better results.
Paws for Trello - The best way to use Trello on your desktop
CAMPR - Open source project management tool with 16 modules
Airtable - Airtable works like a spreadsheet but gives you the power of a database to organize anything. Sign up for free.