There's also postman.com, readme.com, buildwithfern.com, speakeasyapi.dev, useoptic.com, bump.sh along with countless others. It's a very, very crowded market
Many tools in this space have overlapping functionality, but have a lot of differences when it comes to building with them or consuming information from them.
The products take shape around opinionated solutions that are fundamentally different. So, while they "do the same thing", some have better tools for API authoring, some are more usable for non-technical stakeholders, some emphasize performance, some emphasize extensibility, etc.
A good analogy is cars. They all drive, but some have 4WD, some have truck beds.