If you download the .zip file you'll see that Portland (I presume Oregon instead of Maine) is one of the 422 transportation networks included. Or you could just go to the author's website at
http://metro.nanika.net/index-en.html and look.
I've been using Metr0 for years and years (staring on a then-new Palm V...) while travelling. When I made the jump from PalmOS to Windows Mobile a few years back, I first checked to be certain there was a WM version of Metr0 (along with HandyShopper and ePocrates, my other
sine qua non apps) before leaping.
Metr0 is worth double - nay, triple! - the price they ask for it. The interface is a bit idiosyncratic since it's so short on words and it isn't immediately obvious what some of the icons are, but it's quick to learn. It's unbeatable for getting around a strange city while visiting. (It might be similarly wonderful for places where one lives, but my town doesn't have a gas station or a stoplight and public transport consists of streets, so I wouldn't know.)