Brozzler is a distributed browser based web crawler. It was built by the Internet Archive.
From Internet Archive: https://support.archive-it.org/hc/en-us/articles/360000343186-What-is-Brozzler-
Brozzler is our newest crawling technology, built at the Internet Archive.
Brozzler differs from Archive-It's "Standard" crawling technology (Heritrix and Umbra) in its reliance on an actual web browser to interact with web content before that content is indexed and archived into WARC files. Instead of following hyperlinks and downloading files, Brozzler records interactions between servers and web browsers as they occur, more closely resembling how a human user would experience the web. It also uses youtube-dl to enhance media capture capabilities. (as of January 2020 both Brozzler and Standard crawls use youtube-dl).
For more information on how this process works, and the related open-source tools on which it relies, you can review Brozzler’s code and technical documentation in its GitHub repository.
Link to GitHub rep: https://github.com/internetarchive/brozzler
From Internet Archive: https://support.archive-it.org/hc/en-us/articles/360000351986-How-and-when-to-use-Brozzler
When to Use Brozzler:
"If dynamic elements on a page were not captured in a Standard crawl or you're seeing a number of error pages when viewing results in Wayback, running a test crawl using Brozzler is a good next step".