PinsToPaper
pinstopaper.schallert.io
From the page
Saved with the link. Notes from 2007 to 2016 are mostly the page's own words, so this is probably an excerpt.
Pinboard and Instapaper are both awesome services, and they both offer a way to sync your Instapaper items to Pinboard, which can be useful. But what if you want to sync things you bookmark in Pinboard to Instapaper so you can read them later on a client such as your iPhone or iPad? Well then you're out of luck. Until now! PinsToPaper offers a way for you to sync your Pinboard items to Instapaper, specifically your unread ones.