From Josh Abernathy:
Marketplace searches Craigslist for you. Simple? Well yes. But it does more than that too.It remembers your searches so if you tend to do the same searches over and over again, then Marketplace makes life a lot better. Marketplace also lets you search in many regions at once so if you have many regions around you, or you don't care where the results are from, then Marketplace makes life a lot better. And then there's other stuff like filtering and favorites that Craigslist just doesn't have, all of which make life a lot better.The moral of the story: Marketplace makes life a lot better for people who use Craigslist a lot. Made for Mac - Made by a Mac user, for Mac users. It's simple, straight-forward, and fast. Everything a Mac application should be.
Find Anything - Search across multiple regions and categories. Get all the results in one convenient window. Then narrow your search down even more with built-in filtering.
Choose Favorites - Store the best results and come back to them later. Put off until tomorrow what you could do today.