BookNotion is an iOS application that is also available for free.
By upgrading your plan, you can save highlights from multiple books within a month, store an unlimited number of highlights from the Web and X, and synchronize with the same database from multiple devices (such as iPhone and iPad) simultaneously.
|Free Plan||Pro Plan||Premium Plan|
|Price (in US)||free||$3.99/month or $39.99/year||$5.99/month or $59.99/year|
|Kindle: Number of books that can be registered each month||1 book/month||Unlimited||Unlimited|
|Web: Number of highlights that can be registered each month||5 times/month||5 times/month||Unlimited|
|X (Twitter): Number of highlights that can be registered each month||5 times/month||5 times/month||Unlimited|
|Save to same database from multiple devices||✔️||✔️|
|Change the frequency of email delivery and the number of highlights included||✔️||✔️|