I can't speak to the internals of this extension but a few things jump to mind: this works with chrome, fetching.io works with Safari, Firefox and Chrome. This

I can't speak to the internals of this extension but a few things jump to mind: this works with chrome, fetching.io works with Safari, Firefox and Chrome. This works on any OS that has chrome, fetching.io is only self hosted on OSX (otherwise there's a cloud version). This appears to implement its own indexing scheme, fetching.io uses elastic search. Fetching.io has it's own search UI, tagging notes etc, this is integrated directly into chrome. Which is best for you probably depends on your needs. Oh and fetching.io isn't open source ;)