What's a crawler? It's a 15-year-old idea about how to build an index, and is part of the foundation of determining what's good on the web today, for pretty well all search-related services you use.
Wowd takes a different approach, based on an analysis of what we call the "Attention Frontier". This approach has significant benefits in terms of being able to keep up with the volume and velocity of new material entering the web.
You can get the Attention Frontier whitepaper here: http://wowd.com/publications/AttentionFrontier.pdf