Spyglass has a small community that has been building lenses for different topics. You can check out the ones available to download by clicking on "Manage/install lenses" from the menubar icon to open up the "Lens Manager" as seen below.
Community lenses are downloaded from spyglass-search/lens-box.
From here, you can one-click install lenses and the crawler will happily go out and start indexing.
Precrawled and ready to search
All community lenses (and soon private lenses) come precrawled. Spyglass will download the preprocessed content from those sites & use it to update your personal index. Our crawlers currently crawl things on a monthly basis, but this will continue to improve as that infrastructure is built out.