At this point, an app can give people access to their integration via an invite link. Apps can test their integration with real users, get feedback and fix any issues. Once an app feels ready, they can apply to have their integration reviewed by Zapier. If it passes, it goes live. This can be quite a long and intensive process.
For a variety of reasons, some apps choose to leave their integration in invite-only mode and just share access to their customers via the invite link.
To make life easier, we've compiled a list of all the apps we can find that publicly advertise their Zapier integration invite links, so that you can use them in your zaps.