OSC
[Reason: Not much information here! You can contribute by expanding, and proofreading this article, in accordance with the Manual of Style.]

OSC is a way to get different devices and applications to talk to each other. VRChat announced on February 16th 2022 OSC for Avatars[1]. Most commonly used to have body-,eye- and face trackers communicate with VRChat.
OSCQuery
OSCQuery is a protocol to connect OSC applications together easier. Information on how to connect with VRChat with OSCQuery. VRChat also provides a C# library on GitHub.
OSCQuery Libarys currently available to the public:
Typescript with example scripts on github by Jangxx: node-oscquery
Python with examples on the github readme.md vrchat_oscquery, An older vairant also more discriptive: tinyoscquery
Rust implementation with baseline functionally: oscquery
OSC Feature set
OSC Can control a muiltiude of things within vrchat, While primarily focused around avatars OSC has the ability to modify/control some features such as control of the Dolly camera check out the implementation here on the Dollys OSC Intergration page
Access to user params such as 'avatar/parameter/voice' sending the value back as a float 1 will unmute your microphone, A float 0 will mute you.
Chatbox input can be accessed under '/chatbox/input'
Resources
OSC Overview on the VRChat Documentation
Full OSCQuery proposal and how it functions while including example code