Way points can be marked with a tag using a button, with a quick voice record, a text note or by taking a picture. The various button pages and layouts can be customized to suit your OpenStreetMap activities. You can view your current track on top of an OpenStreetMap background.

Note that the official project is run at http://code.google.com/p/osmtracker-android/, this is only an un-official code mirror.
A sister application exists for Windows Mobile: https://launchpad.net/osmtracker