[zsmizzle]

They have a new client that doesn't used Adobe Air anymore.

When asked what technologies they use in the new client:

"HTML/JS/CSS for the UI, C++ for the core functionality. We're planning on publishing a deep dive blog on this during alpha, so make sure to keep your eyes out for it!" [1]

edit: "ggregoire" posted a better answer below [2].

[1] http://na.leagueoflegends.com/na/site/2016-season-update/cli... (See the comment posted by Riot employee "CapnBranFlakes")

[2] https://news.ycombinator.com/reply?id=13438077