Spool is a service that is hoping to bring the best of "read it later" services like Instapaper and Read It Later, and will apply it to other forms of media as well.It's also attempting to do more by being designed for offline use as well.
The first use of Spool is that it serves as a service to read items at a later date, presenting items in an easy-to-read format. This is similar to Instapaper on iOS, only that this is a cross-platform service. There's a browser extension for all the major web browsers. After installing the extension, the link is saved to the user's spool. Then, the user can load up a mobile app, currently available for Android and iOS, and read the content that was saved. New content can be spooled from the app as well, by either searching or visiting a URL directly from within the app.
Now, this gets to the other part of Spool's usefulness; Spool can be used to save videos for offline watching. By loading up the app once an item has been spooled, the site and video is loaded into local memory. This includes Flash videos; the Spool servers can record Flash video and convert them to a format that's viewable on mobile, and able to be watched offline. Videos from Adult Swim and Dailymotion work well with the service. MLB.com doesn't seem to work with Spool's video conversion properly. YouTube videos can't be saved for offline access at this time.
The ability to watch and view offline is a huge part of Spool's utility; by preloading content, this makes it useful for watching videos in places where internet service may be less than ideal or even nonexistent; this is perfect for cell phone users on limited data plans or iPod touch owners. Download videos and content when on wifi, and then watch them whereever. The app is not necessarily optimized for tablets yet.
This app is especially interesting for iOS users looking to easily watch Flash videos on their phone or iPod, and for Android users looking for a service similar to Instapaper for their phones. Spool is free to use, but is currently only available as invite only by registering at Spool's website.