Silk Brush is a port of Tilt Brush to WebXR, with the aim of being as close in functionality to the original as possible. Currently, you are able to use all default brushes, save/load sketches, snapshots, and even do a basic export to .glb. There are a few third party integrations known not to work, and likely some that haven't been tested yet.
It's possible that some data loss may occur between Silk Brush updates! Be sure to visit the Files page and save your work if you need to.
Currently, you can export your model to .glb right from inside Silk Brush, and it will attempt to download it after a 5 second delay. In the event that it doesn't, however, you can browse to the Files page, where all your saved sketches, models, and snapshots are retrieved from local storage and made available to download.
If you find any bugs/missing features, feel free to open an issue on the repo if there's not one already and I'll do my best to address it.