I'm in the process of porting Powder Toy to Android, for use with a variety of smartphones, tablets, etc..
Forgetting platform specific stuff, all PT seems to need is libc, libsdl1.2, libbzip2 and liblua. Android provides a Native Development Kit (NDK) which complements their normal SDK and provides a gcc toolchain and libc.
On top of that some very very helpful person has already set up a build enviroment with working versions of the other 3 libraries ready to go! I found this out of a git here https://github.com/pelya/commandergenius, and set it up on an Ubuntu 11.10 devel enviroment, and succesfully build the demo project and runned it on a Samsung Galaxy S II i9100.
The PowderToy source is still having errors, but is already compiling siginificant amounts, and so this leads me to think that a port will be easily possible.
The SDL library provided in pelya's brilliant buildenv already has built in systems for getting input from the user. I'm thinking I use a pinch zoom gesture for changing brush size, and then just tap to click. I'm not sure about right click yet, but save stamp/load stamp/copy/cut/paste/save scn/load scn can all be put into the built-in android menu.
Thanks for all the positive comments back. I can't work on anything towards an android port this week, but I might make some more progress next weekend. I think I'm pretty close anyway. I'll try to answer a few of your questions.
Firstly Videogamer555, you don't need to jailbreak, root OR use the android SDK to install non-market apps. All you need to do is enable the non-market applications option in the settings menu on the phone. Then just get a .apk file from the net, copy it to the phone's memory, and select it in the file browser to install it. If you don't have a file browser app on your phone, get ES File Browser from the market.
Also Plamoid, I would have to agree with rizorizo that most Android phones are cheaper than the iPhone. I got my SGS2 on a contract for £200 / $311, but the iPhone 4S on the same contract is going between £99 / $154 and £399 / $620 more. Some other Android phones on the same contract are in free handset deals even, and this is the lowest contract price they offer (with a higher monthly cost, even the SGS2 is free).
And no Finalflash50. This isn't going to be for the 3DS. Sorry. If people are interested in a DS port through, I have an R4DS and Black DS Lite and could TRY to port it as a homebrew app.
And rizo and me4502, I'll certainly need beta testers. Thanks for all the help.