I’m not sure how long this has been out, but if you’re using Google Chrome regularly and want access to your Gmail offline (without having to deal with an external client), you can now install the Offline Google Mail browser app.

One plus about the browser app is that it looks like it’s iOS counterpart, so if you want to just check mail without worrying about people IMing you, this is one way to do it. Works really quickly too! I like it!