You cannot install the database server software directly on OS X 1 . Some time ago, Oracle decided not to support it, apparently because it was not used enough to justify the costs involved. I seem to recall that his death nearly coincided with the fact that Apple abandoned its Xserve line, but perhaps I imagined it.
A client such as SQL Developer is a completely different offer in terms of support. SQL Developer is a Java application for which you need to install the JVM / JDK. Java “run it once” may not be entirely true, but it is likely that it will have much less work to support a relatively small Java application than a beast compiled in kind, such as a full-fledged DBMS. Obviously, they need to do some work to get the .app package, and there are some differences between applications and the Windows version, but they do not need to worry about a different architecture, system libraries, etc., How about the JVM problem.
You can use SQL Developer on Mac to connect to a database running on Windows or Unix / Linux, etc., so that it still has a place; the fact that you cannot have a local server running on the same hardware doesn't really matter to most people. It simply allows developers to use a Mac instead of installing them on a Windows or Linux PC.
If you have access only to the Mac, then installing the VirtualBox and one of the prebuilt virtual machine images provided by Oracle is still, as mentioned above , the easiest way.
You can also install Windows or Linux on Bootcamp or on your own virtual machine in Virtualbox, Parallels or VMWare; and then install Oracle natively. Using a pre-created image eliminates the need to learn how to install the database server software, and also makes it easy to return to the previous file - if you really messed up something, you can simply delete it and start again.
If you are worried about performance or power consumption, I would advise you to start with a virtual machine and see how you got there; You can always add Bootcamp later and even move data if you want to go this route.
1 Of course, you can try to hack something; this was done before with 10g, but I have not seen anyone try this recently, so on Yosemite and 11g / 12c it may not be so simple.