The Nintendo DS system is probably the most popular portable game system in the world! Developed from Nintendo's Game Boy Advance SP, the DS has two screens and the lower one is touch-sensitive. It also has a built-in Mic and short-range wireless so you can interact with other players if they're nearby. You can also play online with the Nintendo WiFi service.
Then came the Nintendo DSi with a more powerful CPU and more memory. However, the DSi was not backwards-compatible with the Game Boy Advance although it did have a SD card slot.
With the recent popularity of 3D cinema and TV screens, it's not surprising that Nintendo released the 3DS which features 3D graphics without the need to wear special glasses. There's a 3D Depth slider so you can control the 3D effect and the unit will play normal 2D games, too.
The Wii was designed to compete with existing games consoles such as the Playstation and XBox and it is currently the best-selling games console in the world.