What are some alternatives?
When comparing Tagpacker and Diigo, you can also consider the following products
Raindrop.io - All your articles, photos, video & content from web & apps in one place.
Pocket - When you find something you want to view later, put it in Pocket.
Pinboard - Pinboard is a personal archive for things you find online and don't want to forget.
start.me - A Modern-day bookmark manager. A place for your favorites. A news feed (RSS) reader. A browser startpage. A portal for your team.
Google Bookmarks - With Google Bookmarks, you can save shortcuts to your favorite webpages and navigate to them in seconds from anywhere.
Papaly - Papaly is a simple social bookmarking tool to manage all your links.