If you download the latest version you'll get files known as .arcadedefs. As for playable games there are a good amount, but you need a powerful CPU to run the games (probably a 13th gen i9 (5.6GHZ ) or later for some of the games, but others you can get away with a (4.6-4.8 GHZ)
Games that you don't need the 13th gen CPU
Any 2D game
Bloody Roar 3
Pride GP
Any Gundam game
Wangan Midnight
Moto GP (almost reaches 60 FPS)
Fate: Unlimited Codes (close to 60FPS)
Kinnikuman Muscle GP (close to 60 FPS)
Tekken 4? (tough to say, but it's a playable experience)
Vampire Night?
Games that require the 13th gen i9
Any Soul Calibur game
Tekken 5
Tekken 5 Dark Resurrection
Zoids Infinity (requires the Play ATA build) (might work on a lower end CPU)
Battle Gear 3 (requires the Play ATA build)
Ace Driver 3
Time Crisis 3
Super DBZ
Game that doesn't run at full speed on any CPU as far as I know
Time Crisis 4
Unplayable games
The Idolm@ster (requires a special internet connection?)
Ridge Racer V Arcade Stage (PS2 version works on Play!) (Arcade version missing sound, and controls aren't hooked up yet)
Smash Course Pro Tennis
Pro Yakyuu