I have to echo private messaging. It is clumsy and time consuming to chase people around with a steem transfer memo or on the various chat servers.
Also a framework for an etsy/ebay style marketplace within steemit where goods can be exchanged for steem.
I think I came across a steem auction system a while back. Here is somebody holding auctions:
https://steemit.com/@auctionator
I don't know if it's automated though.