Aimtell - Web push notifications for mobile & desktop
Hiver - Manage Customer Support, Sales and Projects right from your Gmail inbox. Collaborate with Shared Labels, Shared Contacts, email notes, email reminders and email templates
OneSignal - Customer engagement platform used by over 1 million developers and marketers; the fastest and most reliable way to send mobile and web push notifications, in-app messages, emails, and SMS.
MailClark - The Slack bot for external communications
Gravitec.net - Gravitec.net is a smart web push service that lets you boost subscribers through customizable prompts and automatically target your content to the right audience.
Nylas Mail - The Nylas Cloud API powers your application with email, calendar & contacts features. Built-in features for better email, calendar, and contact management.