I’m a Windows/Linux(VM) user. I’d love to try ATOM, but since it’s an OS X-only beta at this point, I’d rather not mess with your curated invite system and request one I’m not currently able to use.
It would be nice if you had e.g. a set of radio buttons or checkboxes underneath the email field, allowing users to select their operating system** (and noting that Linux and Windows are not yet available). That way, when either of those do become available, you have users waiting in the wings… and you’ll have fewer false OS X signups from people who don’t check the FAQ before dropping in their email address.
**If you implement something like this, I recommend including OS X as one of the options, so that it’s clear whether signups are intended for OS X and another OS, or only the selected entry.