For the sake of getting your question answered here it would help to simplify but that aside without firm stats on engagement and sharing it would be difficult to say however with the paid expansion of game like Flappy Bird, Angry Birds I would say viral apps come close to if not over a k-factor of 1.

MachineZone's Game of War is an excellent example.

Others are basically any Zanga or SuperCell game. Most mobile games need to have a very high k-factor to survive with the current cost of acquisition.

Without knowing specific metrics, I would guess: Draw Something, Candy Crush, Clash of Clans, Farmville, and many more

Snapchat, Yik-Yak, Instagram probably, but not Secret. Secret used paid-mobile installs including installs by Indian farms to drive up their app store rankings.