Maverick This box is for Mac OS X 10.9, which is quite old. However, there should be a number of user using and having a lot of trouble. Yosemite This area for Mac OS X 10.10 - Yosemite Mountain Lion OS X Mountain Lion Forums. Lion Mac OS X 10.7 Mountain Lion El Capitan This area for Mac OS X 10.11 El Capitan. Sierra MacOS Sierra has just been introduced in WWDC 2016. Let's talk about this new OS in this category.