Wikicomposer (free version)

Wikicomposer has the standard features of music composition software, but also allows collaboration over the internet. Features include:

* Multi- and Single-Staff playback and looping.
* Familiar editing controls including copy, cut, paste, delete, undo, redo.
* Saving and loading using the midi file format.
* Customizable controls.
* Multiple window support.
* Local and remote persistence.
* Support for external keyboards and mice.
* Basic staff notation.
* Piano roll interface designed for touch-based music composing.
* Full instructions at http://wikicomposer.com/android_instructions.htm

Please note that this is the free version, which differs from the premium version in having a maximum file size for locally-saved files.