Is the upgrade for mavericks still available somewhere?

Hey everyone!

Got a question from a friend who wants to upgrade to mavericks. Is it still possible? I have another friend who told me it is possible, but I can't seem to find the upgrade in the app store anymore. My friend was very confident that there still is a free upgrade available for mavericks. But, I guess, if that's already gone, than is Yosemite an option?