But don't you need Xcode to build stuff for iOS, macoOS, etc.? How do you integrate the two and is it worth it?

I gave AppCode a small spin recently. It worked pretty well — as I've come to expect from JetBrains. It builds and launches apps directly into your device or simulator (presumably using the command line tools of Xcode). There is, however, no integrated Interface Builder, when you want to edit a XIB or Storyboard, it launches Xcode and you do the editing there.

Other than that XIB/Storyboard quirk it seems pretty solid.

EDIT: For me it wasn't worth it. There's something about Java applications that throws me off. I'm not sure if it's the difference interface or the small lag in input or both. (I do use PyCharm since there is no viable alternative in macOS)

I believe you can use xcode command line tools to build using appcode. Haven't used in ages though, so don't quote me on that