Developers fear that if Twitter’s engineers build the same features that they have, Twitter could transform overnight from generous benefactor to arch competitor to their start-ups. 
 
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 The tension is becoming more acute as Twitter matures and develops the resources and desire to buy or build its own version of some of the outside apps. On Friday, Twitter announced that it had acquired Atebits, which makes Tweetie for the iPhone and Mac, and that it had worked with Research In Motion to build an official BlackBerry app. That has other start-ups that make mobile Twitter apps wondering if there is any room left for them. 
 
 “When we launched, Twitter was incomplete, so developers rushed to fill those holes, but eventually we’re going to have to build a lot of features in because they should be there,” Evan Williams, Twitter’s co-founder and chief executive, said in a recent interview. “We want to set those expectations.” 
 
 Fred Wilson, the Union Square Ventures partner who invested in Twitter and serves as a director, echoed that sentiment in a blog post last week that immediately put many developers on edge. “I think the time for filling the holes in the Twitter service has come and gone,” he wrote. “Twitter really should have had all of that when it launched or it should have built those services right into the Twitter experience.” 
 
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 Pete Karl is an engineer who builds Twitter apps at the Digital Influence Group and his own start-up called Lion Burger. “I’m waiting for the other shoe to drop,” he said. “Before, I think developers had the upper hand. But now it’s time for Twitter to try and make some money, and I think they want to create a situation where the scales are tipped more in Twitter’s favor.” 
 
 For the technology industry, this is a familiar story. Giving away technical secrets to those who want to use your product to build their own might seem counterintuitive to most companies, but it is a common path to success in the tech world. Microsoft, Apple, Google and Facebook have all, to varying degrees, opened their platforms this way. 
 
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 It can be a stunning source of growth. 
 
 “Embracing the openness leads to ubiquity, and if you can embrace that ubiquity, you can make money,” said Mark C. Stevens, a lawyer for start-up companies at Fenwick & West in Silicon Valley. 
 
 But invariably, the provider and the developers bump against each other. “That’s how it always is when you develop for a corporate-owned platform,” Dave Winer, software developer, blogger and visiting scholar at New York University, wrote last week. “You have to make peace with that reality before you write your first line of code.” 
 
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 Microsoft, for example, became ubiquitous in large part because of all the tools, like memory managers, that outside developers built. Once Microsoft built memory managers into Windows, those start-ups became irrelevant. 
 
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 Twitter has been unusually free about letting developers tap into its data and technology, through what is known as an application programming interface. Sometimes it gives developers certain tools, like geolocation for Twitter posts, before it uses them on its own site, and developers can use the data and create a site or app without signing any contracts or even alerting Twitter. 
 
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 “The problems we’re solving are so big that we need a lot of people working on them and we need to give them the same level of access,” said Ryan Sarver, the director of platform at Twitter. 
 
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 If developers build something Twitter wants, the company has three options — let it exist separately, create its own version, or buy the start-up, as Twitter did in 2008 with Summize, which created a Twitter search engine, and last week with Atebits. 
 
 “For every platform ever, it’s a question of what should be left up to the ecosystem and what should be created on the platform,” Mr. Williams said. 
 
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 Developers are rapidly learning that truth. Heypic.me is an iPhone app for posting photos to Twitter and to a Web site that shows Twitter photos on a map of the world. 
 
 Twitter has been extremely open with its data, said Heypic.me’s developers, Andrew Seigner and Robert Manson. When the developers asked for more geolocation data, Twitter promptly gave it to them. But they are aware of the risks. “When you go to write a Twitter application, you almost wonder, is Twitter going to come out with the same feature in a month and blow me away?” Mr. Seigner said. 
 
 Their fears were realized when Twitter built a similar site for the South by Southwest conference. They sent Mr. Williams a Twitter message asking if the site foreshadowed future Twitter sites. “If so, you have put us out of business,” they wrote. Mr. Williams responded that it was a one-off site. 
 
 As with all relationships, the tension could worsen once money is involved. That is a concern for companies like CoTweet, a San Francisco start-up that offers tools for businesses to manage their Twitter accounts by tracking conversations with customers and letting multiple employees respond. 
 
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 Companies like Ford and Coca-Cola pay for the service. But Twitter has said it will introduce paid accounts for businesses, including a tool for multi-author accounts that was inspired by CoTweet’s. (CoTweet was acquired last month by the e-mail marketing firm ExactTarget.) 
 
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 Both Mr. Williams and Aaron Gotwalt, co-founder of CoTweet, said they were confident that companies would pay for both services, because they would also offer different things. 
 
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 Twitter has given some hints about where developers will have the most luck. Mr. Williams says Twitter has “a very complementary relationship” with start-ups like CoTweet that build apps for specific audiences. The need to discover people on Twitter and to search for the most relevant posts is so big that many people will be able to do it, Mr. Sarver said. 
 
 Mr. Wilson, who said he was not speaking on behalf of Twitter, said that big businesses would also grow from social games on Twitter and sites that group posts about a certain topic, like movies or job listings. 
 
 One of the goals of the Chirp conference is to shepherd developers in the direction that will be most useful to them — and to Twitter. 
 
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 “There are things that are not good opportunities that people will probably be disappointed if they invest in,” Mr. Williams said. “But we also think there’s a whole bunch of other stuff that we’re not interested in doing or have no plans to do.” 

 The news came this weekend that Twitter has agreed to acquire Atebits, the cleverly named company behind Tweetie, a Twitter client for Apple's iPhone and Mac platforms. This is a huge step, and a glaring indicator, for Twitter as a company--how it'll manifest itself for Twitter the service isn't quite so clear. 
 
 Fred Wilson, a major investor and director for Twitter, hinted last week that Twitter was about to start "filling the holes" in the service. Third-party services, he says, sprung up around Twitter out of necessity: you needed search, you needed a mobile app, you needed a URL shortener, and you needed an image uploader. None of that came in Twitter, and until now, the company was content to let developers fill those gaps. 
 
 But not anymore. Twitter bought startup Summize back in 2008 to create a decent search engine, and now they've acquired Tweetie, one of the best (if not the best) mobile Twitter app. A URL shortener (like bit.ly) and photo uploader (like Twitpic) could well be next. And if Twitter does acquire all the necessary components and offer them as a package, they'll have total control of the medium, which means they'll be able to monetize much more effectively. That strategy will also, of course, leave all the developers who made Twitter what it is today stranded. 
 
 Twitter plans to offer Tweetie free, down from the $2.99 it previously cost in the App Store. That makes two official Twitter apps--BlackBerry just got its own this past week--leaving Android, WebOS, and Windows Mobile with third-party apps for now. That doesn't matter much at the moment (although Tweetie for free is a nice deal), but with their own mobile client, Twitter would be able to provide whatever updates or features they want. 
 
 We should find out more about what Twitter plans to do with Atebits beyond just making Tweetie free, as well as how the company plans to, you know, make money off of the service, at the Twitter event Chirp, this week.
– In another move toward world domination, Twitter has acquired Tweetie, a Twitter client for iPhone and Mac platforms. The purchase is part of Twitter's plan to work on "filling the holes" and eliminate the need for third-party services—and that's causing some tension between the the company and the developers who have built the 70,000 applications that support the microblogging site. The programmers made the apps at no charge to Twitter because Twitter allowed them to make money from advertisers or charge users for their apps, notes the New York Times. But acquiring "all the necessary components" would give Twitter "total control of the medium, which means they'll be able to monetize much more effectively," writes Dan Nosowitz for Fast Company. "That strategy will also, of course, leave all the developers who made Twitter what it is today stranded." Twitter will give Tweetie away for free; it used to cost $2.99 in Apple's App Store.