Windows 10 is free for everyone! But, wait, not really. There's been a lot of confusion about who will be able to upgrade to Windows 10 for free, but this flowchart makes the confusing, shifting policy a bit clearer.
Lifehacker's flowchart shows that if you have a geniune copy of Windows 7, 8, or 8.1, you'll get the free upgrade to Windows 10. The other option to get the free upgrade is if you're running the Windows 10 preview--again, over a valid Windows 7, 8, or 8.1 license.
Otherwise, if you're running Windows Vista or XP or your copy or Windows 7+ isn't genuine, you'll have to pony up for the license. (Insiders can still run beta or non-stable versions of Windows 10, though.)
It's a confusing topic, especially with all the new announcements Microsoft has been making about the Windows 10 licensing, but flowcharts make everything clearer.
[h/t Digital Inspiration]