slidelogo0118081.pngWidget-maker Slide has raised nearly $50 million at a $550 million valuation from two private equity funds, Fidelity and T-Rowe Price, according to the New York Times, with the two firms buying a total of around a nine percent stake in the company.

San Francisco-based Slide has more than 144 million users of its widgets on Myspace and other social networks, and another more than 50 million total (not necessarily active) users of its Facebook applications, according to Kara Swisher at AllThingsD, who first reported that a large round was in the works earlier today.

However, Slide hasn’t, as far as I know, publicly stated significant revenue streams — as is the case with many other Myspace widget and Facebook application companies. A large funding round could mean that the company has proven to investors that it can monetize.

On the other hand, investors may just be impressed with the number of eyeballs Slide has attracted. The company’s Top Friends Facebook application, which lets you designate and display your favorite Facebook friends on your profile page, has 2,483,760 daily active users. Its FunWall application, which replaces Facebook’s “Wall” of messages from your friends on your profile with its own features, such as video-sharing, has 2,762,039 daily active users.

Note: Facebook applications give third-party developers direct access to user data, such as your list of Facebook friends, which companies like Slide can use to make more compelling applications, like Top Friends.

Slide sees itself as a “distributed media company,” relying on its widgets and applications to create new forms of entertainment for social network users. For more, see my interview with chief executive Max Levchin from last June. Its latest efforts include involvement in Open Social (our coverage), a Google-led effort that’s in development, that intends to create a standard means of implementing social networking applications on Facebook rival sites, including Myspace.

Main competitors to Slide include RockYou, which also has popular Facebook applications as well as widgets on other social networks. RockYou claims to have passed Slide as the most popular Facebook app company, as I wrote last month, although it’s not clear if that’s still the case. In late August, Slide claimed the number one spot.

Slide would use the money to expand as well as buy other companies, Swisher says, and has hired investment bank Allen & Co. to help raise the round (the bank, among other things, is also helping Digg shop itself around).

Slide’s previous valuation is based on the approximately $20 million that it raised in 2006 from Khosla Ventures, Mayfield Fund, BlueRun Ventures and Founders Fund (our coverage).

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