Offline readers are on everyone's mind, these days. I made my own. It's a plain vanilla HTML+JS+CSS web application that holds hands with an equally vanilla LAMP+API server. It's probably too soon for anyone else to use but it works. Like it works underground on the subway where the Internet still don't shine.
This is pre-alpha version software. It basically works. Until it doesn't. It does not have any documentation to speak of, yet. No refunds are accepted.
Here is a long blog post describing the current state of affairs.