My idea for a general use, straight-forward, easy to use online marketplace.
It will let you browse listings (including ones from craigslist) in a google map view, so directions and understanding of the location are a cinch. It will have helpful filters that are actually useful, for filtering out the crap.
Listing an item will be a one page process, with support for dragging and dropping photos, and cross-listing onto ebay, amazon, craigslist, and as many other marketplaces as can be added. That way sellers can make sure their product is exposed to as many people as possible as the userbase for whatvr will obviously be small at first. The ability to cross-list will be a big selling point.
Comments and feedback are welcome. Even if it’s something like, “no one needs this and it’s a terrible idea.”