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