Horde - Horde Groupware is a free, enterprise ready, browser based collaboration suite.
RingCentral - RingCentral is the leading provider of cloud-based communications and collaboration solutions for small business and enterprise companies
Roundcube - Web-based IMAP email client
Dialpad - Switch is a cloud-based phone system built for Google Apps users.
Mailo - Mailo is an email client where you can send and receive emails to and from anyone with an email address.
Aircall - Aircall is a call center software of a new generation designed for fast growing companies. Setup instantly and integrates to your CRMs