SlashApi - Build REST APIs fast without having to write any code.
Beeceptor - Unblock yourself from API dependencies, and build & integrate with APIs fast. Beeceptor helps you build a mock Rest API in a few seconds.
Altogic - Build backend apps faster
MockServer - Easy mocking of any system you integrate with via HTTP or HTTPS.
Airtable - Airtable works like a spreadsheet but gives you the power of a database to organize anything. Sign up for free.
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.