Powersnap Alpha is a new, freeware application for Windows PC that allows you to manage pictures/photos in your Flickr account while offline from your desktop computer as well as synchronize them between the computer and your online Flickr account.

From their blog:

Each PowerSnap user can manage all their pictures sitting on their computer the same way they manage their photos on Flickr. And what’s more PowerSnap has a powerful two-way synchronization feature with Flickr. Upload directly to Flickr.com and those pictures popup on PowerSnap. Change captions, tags or permissions on pictures locally and they get updated on Flickr. With PowerSnap you can subscribe to photos from your Flickr friends using simple criteria like tags, sets, date ranges or recent photos.

Download the application here