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.
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.
PushBots - Light SDK for mobile push notifications
SendGrid - Learn why more developers choose SendGrid for their email deliverability service to send transactional emails triggered by web apps. Get started for free
iZooto - Engage your mobile and desktop web users with intelligent web push notifications.
EmailJS - Send email directly from your client-side Javascript code – no server side code required. Add static or dynamic attachments, dynamic parameters, captcha code and more. Start with our free tier!