Games can't be emphasized enough. Grim Fandango and Escape from Monkey Island in the late 90's were the first known corporate games that used Lua. After word got out at GDC, the entire industry started using Lua. Big profile hits like World of Warcraft and Angry Birds make Lua sound like something new in the video game industry, but Lua was already de-facto standard. If you buy a game today, there is a greater chance that it uses Lua than it not.

Wikimedia Foundation (Wikipedia) just adopted and rolled out Lua for its scripting language for MediaWiki end users.

You can browse the Lua code on Wipkipedia here https://en.wikipedia.org/wiki/Special:PrefixIndex/Module: - there is a visual editor, test runner and module system.

Most, if not all, of those are not written in Lua.

Nothing is pure lua, you could probably use GObject-introspection to write a GTK app, but nobody do it.All of these apps have _some_ lua code, but it is nowhere close to 10%, I will give you that.