If you’re a developer who loves to play around with Twitter’s API (Application Programming Interface), or you have been trying to make a serious business out of it, you probably got a very sobering wake up call on Friday, April 10th.

The first rumblings happened on April 7th, when Fred Wilson, a Twitter board member and key investor, wrote a post on his blog entitled The Twitter Platform’s Inflection Point.  In it he suggested that perhaps third-part developers should stop trying to plug holes in Twitter’s service, and instead use the API to build something entirely new on top of Twitter.  Third-party developers started to get nervous something was up, but everything seemed to be sailing fine for a few days.

twitter blackberryThen on April 9th was when the anvils started falling from the sky.  The first major hint that things were changing in the land of Twitter applications was the announcement of the official Twitter App for BlackBerry phones.  Up until now the company seemed happy to allow all of these developers build an endless stream of applications, and Twitter just sat on the sidelines, focusing on improving the core software.  Now that it appears they have the time to look elsewhere, you had to start wondering what they would eye next.

That answer came just a little bit later on the same day when it was announced that Twitter had purchased Atebits, the makers of the popular Tweetie application for both Mac OS X systems and the iPhone & iPod Touch.  Tweetie’s designer, Loren Brichter, will be joining Twitter’s mobile division and helping them prepare an application for the iPad, in the meantime, Tweetie is being rebranded as “Twitter for iPhone” and will be re-released to the App Store for free as opposed to the $2.99 it used to cost.

In one day, Twitter basically killed the the current model of the third-party Twitter developer.  Anyone building a Twitter app for the iPhone, and especially if they charge for it, pretty much just lost their business.  ”Well, I can buy this one Twitter application … or I could download the official one that is free … hmm, decisions.”

I think it’s safe to assume that we’ll see applications for Android-based phones and the Windows desktop in no short order.  (My money is on Twitter buying TweetDeck for the Windows desktop solution)  After that, I still don’t think the company will be done.  Some of the other areas I think they will go after are:

A URL Shortner – Lets face it, Twitter’s limit of 140 character basically made the URL shortening business.  Why should they continue to let services like TinyURL and Bit.ly have all of the business?

A picture service – TwitPic, TweetVid … I think you are all living on borrowed time from here on out.

Mr. Wilson’s post now seems like it was just an early warning to everyone, and the fact two major events happened with apps in the same day I think was meant to communicate that Twitter is not going to be playing around.  They are now in the application game, and they are going to take it very seriously.

I have stated many times in many places that I felt building an entire business on top of someone’s API was fool hearty.  The company could go belly up, they could turn off the API for some reason or they could build their own official application.  You are allowing the entire future of your business to be dictated by the future of another company that you have no control over, and it could be gone tomorrow.  Although I think this case is even worse because the company still exists, but your work is pretty much rendered useless and it’s almost as if you’ve been told, “Thanks for playing, but it’s time you went home.  The adults need their time now.”

I doubt every developer is going to fold up shop tomorrow over this, but I wouldn’t be too surprised to see a bunch of them to be gone within the week.

What do you think, has Twitter basically just taken back the keys to its castle without really shutting everyone down?