Pipedream - Integration platform for developers
Kontact - Kontact is the integrated Personal Information Manager of KDE.
Hoist - Hoist is how you integrate - Meet the microservices platform that talks to APIs
Nextcloud Contacts - The Nextcloud contacts app is a user interface for Nextcloud's CardDAV server.
ifttt - IFTTT puts the internet to work for you. Create simple connections between the products you use every day.
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.