for the Nintendo 3DS is a homebrew recreation of the classic local messaging application originally found on the Nintendo DS. Because the 3DS did not include PictoChat natively (replacing it with Swapnote/Nintendo Letter Box), developers created a CIA (CTR Importable Archive) version to allow 3DS users to chat with original DS and DS Lite consoles via local wireless. Project Overview
Look for the "PictoChat DS-forwarder" or the standalone .cia conversion online (check the usual homebrew archives!). Pictochat 3ds Cia