Bits on Wheels is a native BitTorrent client for the Mac. In fact, it was the first native client released for the Mac. It is written in Objective-C and Cocoa. It is distributed as freeware now, though it once was an open-source project. Bits on Wheels was the first app to introduce a 3D view of the connection swarm. This showed how every peer and seed you were connected to sent data to you. It was a nice view and Vuze now shows something similar.
The application consists of a single window. You can access different panes by clicking on the buttons in the middle of the screen: General, Files, Peers, Pieces and 3D Swarm. The first pane, General, shows information about the torrent and the tracker. It displays the current state of the connection with the tracker, the size of the files to be downloaded, and the state of the transfer. The Files pane shows all the files that will be downloaded, but, unfortunately, you can't tell the app to not download some of the files. This is a feature commonly found in current BitTorrent clients. The 3D Swarm is a nice way of graphically seeing who you are connected to and how many pieces of the torrent you are getting from each seed and peer.
Bits on Wheels hasn't been updated for a long time, and I failed to get it to work. I tried with several different torrents from different trackers, to no avail.