Racing games publish live telemetry for dashboards, motion rigs and wheel displays. Horizon Labs only reads that output: it never injects into a game, reads its memory or edits its files.
UDP streams
The game sends small network packets to an IP address and port you choose, usually your own PC (127.0.0.1). Used by Forza Horizon and Forza Motorsport (Data Out), F1, DiRT, GRID and EA SPORTS WRC. Gran Turismo streams from the PlayStation over the network.
OutGauge
A compact UDP dashboard protocol with engine, pedals and dash lights. Used by BeamNG.drive and Live for Speed.
Shared memory
The game writes its telemetry into a named block of memory that other apps can read. Used by Assetto Corsa, iRacing, Le Mans Ultimate, Automobilista, Project CARS and RaceRoom. rFactor and the truck games add it through a free community plugin.
Why fields differ by game
Each game decides what it sends. Each game page lists the fields Horizon Labs gets, and the Designer flags bindings a game does not provide.