Dokka is like Javadocs but with a much nicer frontend, with multiple export options (HTML, Markdown, etc), and with Kotlin support, if you need it. Just to clarify, it can be used in a pure Java project all the same. You can take a look at the Dokka project here.
Take a look for yourself. I recently forked and published a project and I provide both Javadocs and Dokka. As you see, they both supply the exact same information, but one looks like this:
While the other looks like this:
