DescriptionZwitscher is an Open source Twitter/identi.ca client with support for multiple accounts. It supports most of the basic features and tries to minimize network bandwith usage when e.g. roaming or being on slow networks. Also offline mode is partially supported, where you can write tweets while being offline.
Please report bugs or feature requests here:
or via email to firstname.lastname@example.org as I can't answer back on entries in the market
Github also has the full source - any contributions are welcome.