GPT-3 Playground is the web interface for OpenAI's GPT-3 API. It is likely the original prompt engineering tool that most people have used. As such, it is extremely well known.
GPT-3 Playground provides a clean interface with a few different dials for modifying GPT-3's behavior. It also provides access to different GPT models of varying parameter sizes and prices. They provide free credits, which expire after 3 months.
Sander Schulhoff is the Founder of Learn Prompting and an ML Researcher at the University of Maryland. He created the first open-source Prompt Engineering guide, reaching 3M+ people and teaching them to use tools like ChatGPT. Sander also led a team behind Prompt Report, the most comprehensive study of prompting ever done, co-authored with researchers from the University of Maryland, OpenAI, Microsoft, Google, Princeton, Stanford, and other leading institutions. This 76-page survey analyzed 1,500+ academic papers and covered 200+ prompting techniques.