Muck Rack is an online tool for Public Relation experts. It allow them to find article in various topics and contact relevant journalists.
Muck Rack is a premium tool, therefor it is not free. However many tools like Much Rack trends are free.
Much Rack is a really good addition to your tools set as a marketer. PR could be an extremely powerful channel to spread any kind of product, virtual or physical.
Muck Rack Topics has a "featured topics" section based on Muck Rack's database. More intersting, with the Muck Rack trends tool you can compare trending articles. Use Trends Everywhere keywords comparison tool to cross-validate trending topics from Muck Rack.