Bitrix24 - Bitrix24 is a free (for small businesses) social enterprise platform. It is a united work space which handles the many aspects of daily operations and tasks. Create your own social intranet in minutes!
Vero - Email platform for product, marketing and engineering teams
EngageBay - EngageBay is an affordable all-in-one marketing, sales CRM and service helpdesk software for growing companies to acquire, engage and nurture web visitors to happy customers.
Mailgun - A set of powerful APIs that enable you to send, receive and track email from your app effortlessly whether you use Python, Ruby, PHP, C#, Node.js or Java.
SendX.io - SendX (https://sendx.io) provides remarketing and retargeting tools for web businesses. You can use popups, landing pages, email, web push notification, automation workflows and FB / Google retargeting to drive more revenue.
Aritic Mail - Ariticmail is a transactional email delivery API for applications and enterprises.