Instapaper by Instapaper Holdings, Inc. is a mobile app that gives you the possibility to save articles on your smartphone so that you can read them offline. Even though Instapaper for Mac is not available on the Internet, there are similar tools that you can download and install on Mac. Here is a list of alternatives to Instapaper for Mac.
Feel free to add any alternative to Instapaper for Mac that you know of.
Suggest Alternatives
Readlater is also a nice app to access Instapaper http://macdownload.informer.com/read-later/