R4
The original R4 card has the most basic features of all of the R4i cards and is essentially just a storage device for the Nintendo DS and DS Lite. Users can save games, music and video to the microSD card and use homebrew programs to play them back.
R4i SDHC
The R4i SDHC improved game compatibility so that it supports all Nintendo DS games (up until the release of the Nintendo 3DS). The R4i card also supports MoonShell, a widely-used homebrew multimedia player to improve the playback of music and video files.
R4i SDHC Wi-Fi
The R4i card was updated to improve the Wi-Fi abilities of the Nintendo Dsi with the release of the R4i SDHC Wi-Fi card. The improved Wi-Fi access facilitates a new feature that allows gamers to search for and download games directly to their R4i card without the need to use a laptop or computer to transfer downloaded files via the USB microSD card reader.
R4i SDHC 3DS
The release of the Nintendo 3DS posed problems for R4i owners because the console was not compatible with the old R4 cards. Even the 3DS cartridges are slightly different shapes from the previous game cartridges. Now there is an R4i SDHC 3DS card that claims to be compatible with the Nintendo 3DS and claims to be able to play downloaded 3DS games.