Every console on the shelf
Each console has its own page: what the machine was, whether it plays in a tab or needs the desktop build, and which emulator drives it. This list is generated from the engine, so it cannot name something the deck does not have.
In your browser
Game Boy, Game Boy Advance, Nintendo DS, Nintendo Entertainment System, PlayStation 1, Super Nintendo run through EmulatorJS in the tab. There is nothing to install: upload a game you own and it starts. Save states are written to your own library and are there the next time you open the deck.
On your desktop
The other seventeen need a real emulator, and the desktop build is how they run. It looks for the emulators already on your machine and launches the right one with your game — it ships no emulator binaries itself, which is why it stays small and why nothing here is redistributed.
Your library, either way
The same rule applies on both: you bring the games. Leumas hosts none, links to none and supplies none, and what you upload is visible to you alone.