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.
Outlook4Gmail - Outlook4Gmail provides easy synchronization of your Outlook and Google accounts
KanbanFlow - KanbanFlow is a Lean project management tool allowing real-time collaboration between team members. Supports the Pomodoro technique for time tracking.
Boomerang for Outlook - Boomerang for Outlook offers email productivity tools to track, schedule and send mails at the right time.
Meistertask - MeisterTask is an intuitive task management and collaboration tool.
BlueMail - BlueMail is an email management app for Android, iOS, and Windows.