But the platform has used caps internally all along. Cloudflare makes heavy use of Cap'n Proto (https://capnproto.org/), a capability-based RPC protocol, and recently released Cap'n Web (https://capnweb.dev/), a JavaScript-oriented version of the same idea. The "Cap'n" in both is short for "Capabilities and". (Dynamic Workers sandboxing is based around Cap'n Web capabilities.)
Most successful sandboxes use capabilities, though it's not often something you hear about. Android's IPC system, Binder, is a capability system. And Chrome has a capability-based IPC system called "Mojo".
Implementations include seL4, Barrelfish, Google Fuchsia OS, Capsicum, and a slew of research systems too long to list. It's also worth checking out tangential things like the E programming language and Google's old Caja project.
