HackerRank - <a href="https://hackerrank.com/" > - Palo Alto, CA &amp; Bangalore, India.
About:
Building the olympics of programmers. HackerRank is building an engaged community of programmers across different domains of Computer Science (AI, ML, Databases, security, etc.)
We are witnessing a growth of 32.4% in the active users month over month and the retention rates are soaring. Here's an example for the week of Oct-28 (<a href="http://bit.ly/18vVfpJ" >) - % of users who come back after week-2, week-3 &amp; week-4.
"If 30% of users return to your site after 3 weeks, you're onto something" - Bing Gordon. And we are much more than that after 4 weeks.
Investors: 
We are a part of YC summer batch of 2011, backed by Vinod Khosla and a team of 28 growing incredibly fast in a huge market (<a href="http://on.wsj.com/17stW9f" >)
Enterprise: Our enterprise product (white-labeled version) is used by some of the top tech companies (Facebook, Amazon, Square, Palantir, Evernote, Quora, etc.) for making their interview process effective. That's how we make money right now and we are going to hit a $1M in revenue very very soon.
Hiring: We are hiring for various roles (hackers, sales, marketing, PM's) at both the places. If you're interested, please send me your online profile or resume to vivek [at] hackerrank. It'll be one of the best decisions in your life. Looking forward!
Ask HN: Who is hiring? (December 2013)