What are some alternatives?
When comparing Raindrop.io and Substack, you can also consider the following products
Pocket - When you find something you want to view later, put it in Pocket.
TinyLetter - Start writing your own newsletter instantly.
Tagpacker - A free tool to quickly collect, organize, and share your favorite links.
Buttondown - Buttondown is the best way to start and run your newsletter
Diigo - Diigo is a powerful research tool and a knowledge-sharing community
MailChimp - MailChimp is the best way to design, send, and share email newsletters.