YouTrack - Free, online, easy-to-use, fully customizable issue tracking and agile project management tool your development team will love, by JetBrains. Our cloud or your server.
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.
Jira - The #1 software development tool used by agile teams. Jira Software is built for every member of your software team to plan, track, and release great software.
Nifty - Manage projects, work, and communications in one place.
GitLab - Create, review and deploy code together with GitLab open source git repo management software | GitLab
Redmine - Flexible project management web application