zrok is a similar capability (though it can potentially do a lot more). OpenZiti is definitely a more complex project. In fact, zrok was built on top of OpenZiti.

We did this as Ziti provides a platform to develop secure by default, distributed applications quicker, which is why zrok has been built by only 1 developer across about 18 months and is almost feature parity with Ngrok (which has been developed by many people for almost 10 years).