Shadow Workers is a free and open source C2 and proxy designed for penetration testers to help in the exploitation of XSS and malicious Service Workers (SW). A successful exploitation allows you to browse on the targeted application as the victim(s), as long as the SW (agent) is active. A victim does not have to have a browser tab open in the application for the agent to be active.
TrustedSec Blog posts on the tool:
https://trustedsec.com/blog/persistence-through-service-workers-part-2-c2-setup-and-use
This tool is released under the MIT License.