WonderPush

WonderPush is a platform offering mobile and web push notification, in-app messaging for iOS, Android and websites. The solution enables thousands of developers and marketers to send more than 350,000 notifications per second.
WonderPush pricing starts at €1.00 per month and includes a 14 days free trial.
Its pricing is designed to scale with the business and lets users send unlimited notifications and in-app messages without any engagement.