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.
Mergify - Stop merging your pull requests manually
Corrello - Dashboards for agile teams using Trello
Mergefly - A modern UI for GitHub pull requests
Toby for Teams - Better bookmarks, now with collaboration baked in 🔖
PR Patrol - Monitor code that matters to you