Not a lot of startups have been known to launch an eight-figure investment fund three years after hitting the scene, but then again Slack Technologies Inc. is not exactly the typical up-and-coming Silicon Valley venture either. Its collaboration service has become a staple of day-to-day work at thousands of the world’s biggest enterprises and now boasts over two million daily users, adoption that the new financing arm will aim to expand by encouraging more third party support.

Slack will split its investment efforts between fostering integration with conventional business software and spurring the development of new applications designed specifically to complement its built-in communications capabilities. Falling into the latter category is Xoxo Inc., one of the three startups to have received capital from the fund on launch, which offers a free utility called Howdy that can automate certain common activities like checking up on the progress of a project. It’s also the developer of the Botkit, an open-source framework that is rolling out in conjunction with the announcement to help others build their own extension services for the collaboration service.

The toolkit provides pre-packaged code for handling some of the more difficult tasks involved in integrating a piece of third party software into Slack, including authentication and message processing. Applications that use the framework will be listed alongside all other supported software in the new Slack App Directory, a marketplace modeled after Apple Inc.’s App Store that allows users to search for partner-made services by category and popularity.

The startup’s ambitious ecosystem initiative should go a long way toward leveling the playing field against Atlassian Inc., which likewise maintains a catalog of third party integrations for its rivaling HipChat service. But the gap won’t be easy to close. The Australian company boasts more than 2,000 apps in its marketplace compared to the Slack App Directory’s just over 160 and recently hit $120 million in partner sales, momentum that the $431.8 million in capital raised through its public offering last week will no doubt be used to accelerate.

The rivalry between the two collaboration giants should make for an interesting next few quarters in the developer ecosystem. But the biggest winners will be the end-users, who are set to receive a raft of new third party integration options as Slack and Atlassian ramp up their efforts to one-up each other.

Image via jeferrb