For Android, the market can be avoided by just offering the .apk file (e.g. you can self-host the .apk and only share the link with a select group, or if that's not secure enough, require a unique key to unlock the app once it's loaded).

More here: http://www.google.com/search?q=android+sideload+apk

P.S. Has anyone had success developing an Android app with Google's App Inventor tool (http://appinventor.googlelabs.com/about/index.html)?