Our school is moving to more active use of Lexile scores for reading selections. The Lexile website has a nice analytic tool which allows you to upload text (after you create a user account) for analysis. The pain in this process is that A) you can only do it from the Lexile.com website, and B) it has to be plaintext.
So much of the web is rich text now that it's difficult to create plain text files. It's even difficult to do so using Notepad or TextEdit on PC and Mac because they want to save as rich text. Most teachers don't realize that there is a particular process that must be used.
Head over to the dedicated page to install (or play with) the app.
Fair warning - this may never be updated again. Use it til it breaks. (And share it with your friends.)