Linden Lab went through a period when they envisioned a 3D web, where the same client would talk to multiple virtual worlds. Around 2011, they backed off on that. But others went on, and to the surprise of Linden Lab, Open Simulator was developed. The Second Life simulator is proprietary, while the client is open source. Both are in C++. Open Simulator is in C#, and it's roughly compatible, although totally different internally.
I've been writing a Second Life / Open Simulator client in Rust for the last year or so, so I know the wire protocol. VWRAP seems to be an attempt to define a more portable wire protocol with roughly the same information.
The current Second Life wire protocol has two parts, events via binary UDP messages, and assets via HTTP. The UDP message formats are defined here.[1] This is a painful system. Both ends have to use exactly the same message template file, because messages do not contain length information. You have to parse each message perfectly just to find the next message. This makes adding new messages very difficult. No new messages have been added in years. That's one problem VWRAP was intended to solve.
Assets come in from ordinary web-type servers, and complex ones are encapsulated in Linden Lab Serial Data Protocol, which is documented and has multiple implementations. Those are reasonably straightforward to deal with.
The conceptual problems of interoperability are much tougher. There are some metaverse standards organizations starting up, but they're working more on diversity, inclusion, and safety than wire protocols. Content standardization is making progress. Content standardization seems to be settling on some subset of GLTF/USD formats. NVidia is pushing that, and the major tools (Maya, Blender, Unity, Unreal) all speak it. That's a file format, not a wire protocol.
Enough standardization to allow portals between virtual worlds would be a big win. There's talk about this, but not much is happening, except in the Open Simulator ecosystem, where it works now.
One company, Ready Player Me, has an interesting concept - outsourced avatars. Avatars are created on the Ready Player Me site. Cooperating games have a module which renders such avatars, going out to Ready Player Me for the assets. This gives Ready Player Me a lock on avatar appearance and wearable items. For now, this is free. For now. "Wolf3D has the right to amend the Terms unilaterally." Some smaller games are using this, but the big studios have mostly stayed away. If that catches on, those guys have control over the air supply of the Metaverse.
[1] https://vcs.firestormviewer.org/phoenix-firestorm/files/tip/...