What are some alternatives?
When comparing Knotes and Clippings.io, you can also consider the following products
Readwise - Effortlessly rediscover and organize your Kindle highlights
Klib - Kindle & iBooks Highlights Manager
Booxia - Save & review highlights from Kindle & Web pages
Unhoard - Rediscover things from your Pocket every week
Nimbooks - Host all your digital reads in one place
Hazel - Lighweight update server for Electron apps