OneSignal

OneSignal is a hosted messaging service. An app adds a client SDK, and the service sends push notifications, emails, in-app messages and SMS to the app’s users, with campaigns built in a dashboard or sent through an API. Journeys, segmentation and analytics are part of the same platform.

The docs name no self-hosted version. Its client SDKs cover Android, iOS, Flutter, React Native, Expo, Unity and the web.

Worth knowing

Plans are listed on the pricing page. The free plan is one of them, and the higher plans are sold through a sales contact. Two-factor authentication and audit logs are listed on the higher plans.