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®
Corrello - Dashboards for agile teams using Trello
Paws for Trello - The best way to use Trello on your desktop
Toby for Teams - Better bookmarks, now with collaboration baked in 🔖
Airtable - Airtable works like a spreadsheet but gives you the power of a database to organize anything. Sign up for free.