While the official Nintendo DSi Shop closed in 2017, you can still install the original on a modded Nintendo 3DS or 2DS using a CIA (CTR Importable Archive) file. This is particularly popular for users who want to connect to community-run servers like Sudomemo . Installing Flipnote Studio (DSi) on 3DS
Since the official Flipnote Hatena servers were retired in 2013, many users use to share animations: flipnote studio dsi cia