However, there are free "homebrew" games you can download and these are typically released under Creative Common licenses, as freeware or as open source; the emulators you find for the N64--as well as other consoles--are open source.
Finding ROMs of popular games like Sonic or Vectorman might require a little homework, but if you are looking for independently made games or homebrew games, you'll probably have better luck.
This emulator was first used to play homebrew games on the PC, but new releases increased the capability to play ROMs of popular titles like the New Super Mario Bros. and WarioWare Touched!
Since the Sony PlayStation 2 has been available for a number of years, the "homebrew" and "hacking" communities have had a lot of time to work on a solution for playing burned video games.
Homebrew solutions come in two main forms for the DS: one is a cartridge that goes in the primary DS slot and the other is a cartridge that goes in the secondary GBA slot.