What are some alternatives?
When comparing Pangolin and Marker.io, you can also consider the following products
InSite Feedback - InSite Feedback provides instant feedback and reviews of your website.
UserSnap - Usersnap Track is your central place to organize user feedback and collect bug reports. One screenshot is all it takes. Get rid of endless email exchanges and coffee-stained sticky notes. Your new life is awaiting you!
BugHerd - BugHerd: The Visual Feedback Tool for Websites
Webscope - Get live website feedback from your clients
Jira - The #1 software development tool used by agile teams. Jira Software is built for every member of your software team to plan, track, and release great software.
TrackDuck - Visual feedback for web design and development.