Grapevine is a free app. How do they run their startup?

Pardon me for being so naive here. I want to understand this new type of startup trend.

1. What’s the source of motivation for their employees to stick to their jobs?
2. How do apps like these think of monetizing? There is no ad, no paid feature per say.
3. Grapevine has probably built some kind of a platform. But how is this different from platforms like twitter, facebook or any other social media platform?
4. How much money do you think has been invested into building apps like this?
5. The DAU of this app based on my wild guess must be around 5K. I may be completely wrong here.
6. What according to you is the current valuation of grapevine?
7. Saumil Tripathi, the founder of grapevine is ex-google employee as per his LinkedIn profile. There is no mention of any other any other startup he owns.
8. Grapevine has a team of 10 employees (as per Saumil’s post a few weeks back) How do these guys make money?

I’m awestruck by the guys working in grapevine. Building an app of this quality with no monetization in sight!

Pounce on this thread with your thoughts guys!