Jenkins - Jenkins is an open-source continuous integration server with 300+ plugins to support all kinds of software development
Thunderbird - Thunderbird is a free email application that's easy to set up and customize - and it's loaded with great features!
Travis CI - Focus on writing code. Let Travis CI take care of running your tests and deploying your apps.
Microsoft Outlook - Organize your world. Outlook’s email and calendar tools help you communicate, stay on top of what matters, and get things done.
CircleCI - CircleCI gives web developers powerful Continuous Integration and Deployment with easy setup and maintenance.
eM Client - eM Client is a fully-featured email client for Windows and macOS with a clean and easy-to-use interface. eM Client also offers features for calendars, tasks, contacts, notes, and chat.