If something works with NVDA and Jaws, it usually works with VoiceOver, Talkback etc too. Differently, but it should still work.
If you have any Macs or iOS devices around, it's easy to test with VoiceOver as that comes with the system.

In theory, if you follow the various W3C guidelines, you should work fine with every screen-reader on the market. I only use NVDA myself, but from what I hear, JAWS and NVDA are pretty similar; they have similar approaches to things, run on the same OS, and call APIs in similar ways. The big differences happen from one platform to another. For example, VoiceOver on OS X is totally different from NVDA on Windows; the OS X operating system has totally different APIs that work in completely different ways, and Voiceover thus presents information in different ways from NVDA. Same goes for Orca on Linux. Your best bet is to just do what your doing; if it works on NVDA and JAWS, it should work on OS X and Linux 99% of the time.

For the most part, following the WCAG 2.0 guidelines is your best bet for full universal excess ability across windows and Mac. Don't cut corners, try to stay away from JavaScript, use and learn aria, and in general keep things simple. It's all based around robust semantics in the markup, so keep things structured appropriately, label everything appropriately, use alt text on images as necessary, hide things that aren't necessary for screen readers to interact with, follow the guidelines, and you should be totally fine.