I also got tired of viewtext.org being frequently offline and hacked the old readability source code to allow passing in HTML as an argument, this allows you to use it on arbitrary HTML and not just on the current window.document.

This has only been tested on my HN chrome app, YMMV: https://raw.github.com/balaclark/hacked-news/master/readabil...

http://www.feedsapi.org is an alternative, paid alternative and also has a json & xml API