“Techmeme is our go-to primary source,” said Marshall Kirkpatrick, an editor and lead blogger at ReadWriteWeb, a tech blog. He visits Techmeme up to 15 times a day on his computer and phone, and requires his blog’s other writers to track it for breaking news.

Some aggregation sites, like Google News, rely on software to crawl the Web and spot key words in news stories. This model is fast, but it often misses nuances and different interpretations or developments on the news.

Others, like Digg, ask anyone on the Web to suggest stories, and many readers use Twitter as a user-generated newsfeed. These sites can be amateurish (the link that got the most votes on Digg on a recent morning was a video of someone falling on rollerblades).

Still others, like Arts & Letters Daily and the Romenesko news media blog of the Poynter Institute, rely on human editors to gather the important stories of the day. Individuals who filter the news bring more editorial expertise, but they are often slower and less comprehensive than a computer, and it is difficult to expand the service to other topics.

“We’re more interested in quality than we are in beating other people with deadlines,” said Denis Dutton, the editor of Arts & Letters Daily, which is owned by the Chronicle of Higher Education. It posts three new stories a day and six on Mondays, and sometimes they are a few days old.

Techmeme combines all three strategies, automatically searching the Web, employing editors and accepting tips from readers. Other sites, including Blogrunner, an aggregation site owned by The New York Times Company, also use several of these strategies.

In 2004, Mr. Rivera had received a doctorate in computer science and was working at Intel when he observed that it was difficult to monitor all the blogs sprouting across the Web. He started Memeorandum as an automatic aggregator searching for the political news articles that were most linked to by other sites.