The android app should host a webserver that files can be downloaded from/uploaded to.

[nymx]

This would make transfer between device with NitroShare and a device without NitroShare really easy!

[nathan-osman]

This is planned for a future release. Support for transfers to and from devices without NitroShare entails a lot of security issues, so it won't likely be implemented in the next couple of releases.

[UsernameInvalidException]

You might consider using NanoHTTPD for this purpose, since there's already a working implementation in Java IIRC

[masonh]

As an alternative for sending files, try Share via HTTP https://github.com/marcosdiez/shareviahttp