Navfree lands for Android, brings crowdsourced offline voice-guided navigation to many places1
The difference is in maps - Navfree relies on the crowdsourced project OpenStreetMap, which is described as the Wikipedia for GPS navigation. With more than two 3.7 million members of the project, Navfree allows them to enter map comments and fixes at navmii.com, which are further used to enhance the experience that users are already pretty content with.
For places with free maps the navigation software offers routing almost on par with dedicated satnav solutions like TomTom or Garmin, with somewhat poorer functionality, but all basics are there and you can't beat free.
source: Navfree (Android Market)