Aggregators are websites or software that collect specific types of information, like RSS feeds, from multiple online sources and display them in one place. RSS allows users to track updates from favorite websites. Aggregators are useful because they bring information to users from wikis, blogs, social networks, news, and Twitter, rather than requiring users to visit each site individually. Popular aggregators include Netvibes, feedly, NewsBlur, My Yahoo, PageFlakes, and Protopage.