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.
Thunkable - Powerful but easy to use, drag-and-drop mobile app builder.
Truepush - Unleash limitless possibilities with Truepush and save up to $600 monthly. Free up to 10K Subscribers on all features.
MIT App Inventor - App Inventor is a cloud-based tool, which means you can create apps for phones or tablets right in your web browser.
PushCrew - Push Notifications for Websites
Bubble.io - Building tech is slow and expensive. Bubble is the most powerful no-code platform for creating digital products.