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.
Request inspector - Debug web hooks, http clients
Ocamba - An all-in-one marketing solution designed to help you increase your revenue with push notifications, web & mobile analytics, and ad exchange technology.
MockServer - Easy mocking of any system you integrate with via HTTP or HTTPS.
Braze - Braze is an engagement platform that empowers growth by helping marketing teams to build customer loyalty through mobile, omni channel customer experiences.
Webhook.site - Instantly generate a free, unique URL and email address to test, inspect, and automate (with a visual workflow editor and scripts) incoming HTTP requests and emails.