We are working on startup: http://intigi.com. You can subscribe to your RSS or Twitter feeds and then filter the feeds by your interests (i.e., using keywords).

In terms of social features, you can make any interest public and share it with others. You can also follow or fork any of the public interests (like Github).

We are in early stages with the social features (and overall product) and would really appreciate any feedback/input! You can email me at mjfern@intigi.com or use the feedback button throughout the site.

Thanks in advance!