Herbivore is not so catchy as a title?
ResearchGate.
You have mentioned an observation that I have wondered about off and on, i.e. articles published behind a paywall & also free on ResearchGate.
Wikipedia offers this : ResearchGate - Wikipedia
ResearchGate uses a crawler to find PDF versions of articles on the homepages of authors and .[publishers.[5]: Q6 These are then presented as if they had been uploaded to the web site by the author:[5]: Q7, Q8 the PDF will be displayed embedded in a frame, and only the button label “External Download” indicates that the file was in fact not uploaded to ResearchGate.[citation needed].
It has also been criticized for copyright infringement of published works.
In September 2017, lawyers representing the International Association of Scientific, Technical, and Medical Publishers (STM) sent a letter to ResearchGate threatening legal action against them for copyright infringement and demanding that they alter their handling of uploaded articles to include pre-release checking for copyright violations and "Specifically, [for ResearchGate to] end its extraction of content from hosted articles and the modification of any hosted content, including any and all metadata.
Subsequently, Coalition for Responsible Sharing (CfRS) reported that “ResearchGate has removed from public view a significant number of copyrighted articles it is hosting on its site”.[55] CfRS also confirmed that “not all violations have been addressed” and as such, takedown notices have been issued.[56]
ResearchGate has managed to achieve an agreement on article uploading with three other major publishers, Springer Nature, Cambridge University Press and Thieme. Under the agreement, the publishers will be notified when their articles are uploaded but will not be able to premoderate uploads.[57]
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I generally support Copyright issues especially because the author of a photo finds his/ her work used sometimes without even an attribution.
Some aspects of copyright, e.g those USA laws for the benefit of corporations, not individuals, which have been forced on everyone, I am not enamoured by.
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Later… this publication , Nimis & Martello 2003, A second checklist of the lichens of Italy with a thesaurus of synonyms, is a book. It has been downloaded to Researchgate as a pdf. I thought I’d save the link, but Safari blocked it. Perhaps Safari has blocked all Researchgate links.