Kontact - Kontact is the integrated Personal Information Manager of KDE.
Jenkins - Jenkins is an open-source continuous integration server with 300+ plugins to support all kinds of software development
Nextcloud Contacts - The Nextcloud contacts app is a user interface for Nextcloud's CardDAV server.
CircleCI - CircleCI gives web developers powerful Continuous Integration and Deployment with easy setup and maintenance.
Google Contacts - Google Contacts is Google's contact management tool that is available in its free email service Gmail, as a standalone service, and as a part of Google's business-oriented suite of web apps Google Apps.
Travis CI - Focus on writing code. Let Travis CI take care of running your tests and deploying your apps.