os.startfile can be implemented on other OS'es besides Windows relatively easily (although the operation parameter should probably be limited to Windows; it can be implemented elsewhere, but is probably not worth the trouble).

On Unix-like operating systems besides OS X, an attempt to use xdg-open can be used and will attempt to open the file in a chosen program; this is the freedesktop.org standard open utility. See also http://linux.die.net/man/1/xdg-open and https://wiki.archlinux.org/index.php/Xdg-open (not specific to ArchLinux).

On OS X, open can be used, with similar results to xdg-open (in fact, xdg-open seems inspired by it). See also https://developer.apple.com/library/mac/documentation/Darwin/Reference/ManPages/man1/open.1.html.

Duplicate of Issue 3177, which has quite a bit of discussion and some patch proposals.  You might want to add yourself as nosy to that issue and see what you think of the proposals (I did not read through it to see what the status is...there hasn't been any activity on it for a long time, so it is ripe for someone new to pick it up and carry it forward).

I'm not going to reopen that can of worms.

Sorry to waste your time.