ITA Matrix by google will allow you to do that. Be aware however that the Airfares on the matrix are coming from a cache so may not be very accurate.

You can do a search to say from Seattle to six different cities. The program will give you the best pricing based on those routes and the days you choose.

The Website does not actually sell tickets. It does allow you to print out the information you need to take to a travel agent to be able to re-create the itinerary. As they are working from Cache in many cases the seats are gone, are restricted to sales in certain locations, or have combinations of airlines that are not allowed by the airlines.

It is actually a very good tool for finding alternative options for flight routes. Check the answers with an OTA like Future.Travel and you can quickly check to see if the suggested routing is available for ticketing.