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.
BitBucket - Bitbucket is a free code hosting site for Mercurial and Git. Manage your development with a hosted wiki, issue tracker and source code.
Notion - All-in-one workspace. One tool for your whole team. Write, plan, and get organized.
GitHub - Originally founded as a project to simplify sharing code, GitHub has grown into an application used by over a million people to store over two million code repositories, making GitHub the largest code host in the world.
Slack - A messaging app for teams who see through the Earth!
GitLab - Create, review and deploy code together with GitLab open source git repo management software | GitLab