Unpaywall.org's API knows of more than 23 million DOIs for which a legal Open Access copy is available, either as green or gold Open Access. Whenever my app comes across a DOI, it will query the unpaywall.org API to see if an Open Access copy might be available elsewhere. The app itself does not track you, it does not collect usage statistics and it won't cost you a penny, as the APIs I use (unpaywall.org and core.ac.uk) are available free of charge to me.
When it comes to your privacy, you should not trust just any stranger on the internet! To help you decide for yourself the source code for my apps is available at Github, where you will be able to review it, if you are so inclined.
My contribution - in all honesty - is a thin wrapper around the APIs of some Open Access champions of the best kind. Standing on the shoulders of giants has a whole new meaning that way. The thought of charging for this, seems rediculous to me and thus I don't!
In Safari (macOS) it couldn't be simpler. As soon as you see an orange badge at the top right of your screen, this document is avialable as Open Access at a different location. Simply click the badge and it'll take you there. If you see a green badge, you are at the best Open Access location already! If you highlight some text and ctrl-click you'll be able to send your selection as a search to base-search.net or core.ac.uk!
Things are a little more involved on iOS, but only a little! When you hit a paywall at a publisher, tap the share icon in Safari and select OA Helper. The app will try to identify the DOI of the document and search unpaywall.org API for an Open Access copy. If successful, you'll see details, such as the Open Access location and a big green button will take you there. When you select some text and tap "share", you will be able to send your selection as a search to core.ac.uk.
I love iOS and iPad just as much as you do. My app makes Open Access as simple as 1, 2, 3
Send me an eMail: firstname.lastname@example.org
If you write for support, remember to describe your problem in detail and please remember this is my hobby
Read the FAQ for some questions I get often and for informatoin I really want you to see.