I'm one of the founders of Crowdbooster, a YC S10 company built on Twitter.

Twitter, and specifically the API team, has worked hard to come up with guidance for where they think there are opportunities in the ecosystem.

They have very clearly told third-party developers to stop making Twitter clients [1]. Twitter wants to own the display of tweets since they are focused on making advertising their core business.

But there are definitely opportunities if you think beyond just making clients. The five main categories that Twitter specifically mentions are: Analytics, Curation, Content, Publishing, and Enterprise [2].

To echo PG, there are definitely still big companies to be built on top of Twitter. You just have to think big to begin with.

[1] https://groups.google.com/forum/#!topic/twitter-development-...

[2] https://dev.twitter.com/blog/ecosystem-showcase

We're probably not as hot on it, but I still think there are big new things to be built that will rely on Twitter.

Hi PG, we submitted the application and included an idea for a business/enterprise application built on Twitter. While it is not the main idea with which we're applying to YC, it is something I've thought about for a long time.

This Twitter app is really something I wish I have. I have also seen other companies using Twitter in the context described in my application. I had even posted this idea on Facebook so that someone else could build it, but until now, it doesn't exist yet.

Please check out our application and let me know what you think.

It has been updated since the iPad was not released till 2010 and there is an RFS: http://ycombinator.com/rfs6.html

For what it's worth, they still ask on the YC app if you are applying in response to an RFS.

Hard to tell, but that's probably a good indicator that they still are interested in them.