It's the infrastructure for self-hosting web apps. So, on top of Sandstorm, you could get a Dropbox-like app, or a Google Docs-like app, or a Flickr-style app,

It's the infrastructure for self-hosting web apps. So, on top of Sandstorm, you could get a Dropbox-like app, or a Google Docs-like app, or a Flickr-style app, hosted on a box that's in your living room or on your own server in a colo. So instead of uploading your photos to Flickr and sending Flickr links to your family, you would upload your photos to PicShare.StevesHomeComputer.com and send those links to your family, keeping all of your data in your control and not subject to Flickr shutting down one day. It makes sense for some services that are fundamentally user-fragmented (File backup/Evernote/Flickr) but less sense for things that require multiple users to be credentialed like social networking, since social networking structurally benefits from everyone being on the same service.