From the Super Mario Wiki
Wario's Laptop is what Wario uses to set up his microgames in WarioWare, Inc.: Mega Microgame$!. The menu and select screens are also made to look like it is on the Game Boy Advance screen. Wario has all of the microgames stored on it and when he unlocks a new one by playing it, it appears on the screen with all of the minigames.
Wario's Laptop re-appears in the intro sequence of Game & Wario with Wario typing on it after calling his friends.