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.

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Yes, there are several examples of games and apps that have achieved a viral coefficient (k-factor) greater than 1. Here are a few notable examples:
1)Candy Crush Saga, a popular mobile game, achieved viral growth by integrating social elements.
2)TikTok, a short-form video app, has seen explosive growth and a high viral coefficient.
3)Snapchat, a multimedia messaging app, gained popularity among younger demographics and had a high viral coefficient.
4)WhatsApp, a messaging app, experienced rapid growth and achieved a viral coefficient above 1.
It's important to note that achieving a viral coefficient above 1 is challenging and not all products will experience such rapid growth.

Yes, a K-factor above 1 is the holy grail of viral growth — and while sustained K > 1 is rare, there are well-documented examples of products that hit it, at least during certain growth phases.

Here are some of the clearest examples:

1. Hotmail (1996): The original viral growth story. By appending "Get your free email at Hotmail" to every outbound email, they grew from 0 to 12 million users in 18 months. The built-in signature meant nearly every email was a referral touchpoint — a textbook K > 1 loop.

2. WhatsApp: Group messaging has a natural viral mechanic — one user invites multiple contacts, each of whom joins and potentially invites more. In markets like India and Brazil, WhatsApp's K-factor was well above 1 during peak growth.

3. Dropbox: Their referral program (give 500MB, get 500MB) drove a reported 3900% increase in signups. That's a mechanically engineered viral loop that pushed K well above 1 during the referral campaign period.

4. Among Us (2020 resurgence): Players literally cannot play without inviting friends into a session. The game mechanic itself is the viral loop. During the COVID period, it achieved explosive K > 1 growth driven purely by organic referral through social streams and group play.

5. Wordle (pre-NYT acquisition): The shareable tile results mechanic (without spoiling the answer) was a near-perfect passive referral loop. Each share drove measurably more new users than were needed to generate the share.

Key takeaway: K > 1 almost always comes from a mechanic that's baked into the core product usage, not bolted on as a referral program. The best ones make sharing feel natural or unavoidable.

Happy to discuss how to design a viral loop into a specific product you're working on.