Tumbl.in, a project hatched in a weekend of coding, and FriendShuffle, a similarly scrappy website launch, have been making waves recently for their simple but compelling takes on content discovery on social networks.

Both emulate the serendipity of StumbleUpon, a lesser-known content-sharing site that nonetheless generates big traffic for sites chosen by its users. Instead of drawing on their own user bases for links, however, the new sites trawl feeds from Twitter and Facebook

Tumbl.in and FriendShuffle have you connect your Twitter account. Both then take you to random links chosen from those being shared by your friends and followers on the service. FriendShuffle adds links from Facebook as well.

iPad apps like Flipboard and Pulse let you sift through your Twitter stream in interesting ways, aiming for a more controlled magazine experience. The uncertainty of not knowing what you could see next can make for many hours of futile fun, and points to an interesting dichotomy: While it’s useful to scroll through a stream or flip through pages in reverse chronological order, the drudgery of catching up doesn’t match the fun of finding things one didn’t set out to look for in the first place.

It’s this spontaneity that has bought hard-earned success to StumbleUpon, which crossed 10 million users back in June. Other examples of serendipitous content discovery abound, like the recent Google Instant-meets-YouTube service YouTube Instant, which got coverage from many major outlets around the country and had its creator accepting a job at YouTube.

Tumbl.in and FriendShuffle mixes spontaneity with social connections, so their content originates from people or brands one is already connected to, which makes the results even more potentially relevant to the user.

Tumbl.in was created by UCSC student Suchit Agarwal and Blippy engineer Rahul Thathoo. The duo originally developed it at a hackathon event held in conjunction with technology blog TechCrunch’s recent disrupt conference. They’re currently working on adding additional features such as introducing topic verticals through links shared by Twitter’s Suggested Users, content-specific discovery (for example, a Tumbl.in just for video links), and an iPad app.

FriendShuffle’s developers are more secretive. Developer Chase Sechrist apparently launched the service with a tweet last week. Ustream.tv employees Matt Schlicht and Mazyar Kazerooni have been actively tweeting about the service recently. Kazerooni told a friend he’d “put out a new website” and Schlicht recently answered a question about the service shortly before the official FriendShuffle Twitter account did.

Both Tumbl.in and FriendShuffle are currently privately funded.

DB2010Getting content noticed is a challenge for everyone making apps. Join us at DiscoveryBeat 2010 and hear secrets from top industry executives about how to break through and profit in the new cross-platform app ecosystem. From metrics to monetization, we’ll take an in depth look at the best discovery strategies and why they’re working. See the full agenda here. The conference takes place on October 18 at the Mission Bay Conference Center in San Francisco. To register, click here. Hurry though. Tickets are limited, and going fast.

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