Snow Leopard port of Word on the Street for iPhone
Word on the Street lets you leave notes wherever you are. You can also search for notes that other people have left nearby. You can rate locations, tag them, and share them with people, even if they don't have an iPhone.
It also connects you with volunteer opportunities with charities and non-profits in the locality.
This is an alpha Mac port of the iPhone program and is currently read only. All of the iPhone features will be ported in future versions.
Note: requires snow leopard