[[caption-width-right:350:Meet Nikki: Your helpful resident VideoGame/{{Mii}} of Swapnote]]

''Swapnote'', or ''Itsuno ma ni Koukan Nikki'' in Japan (''Nintendo Letterbox'' in the EU, ''Nintendo Mailbox'' in some other areas) was a free messaging app on the UsefulNotes/Nintendo3DS released in late December of 2011. Unlike other messaging apps that let you give small blurbs of text, you essentially send scribbled notepad messages which are "redrawn" to the recipients, and even have the ability to draw [[UsefulNotes/ThreeDMovie in 3D]] along with attaching 3D pictures or sound bites. These messages can be sent to friends online via [=SpotPass=] or [[SocializationBonus person-to-person]] [=StreetPass=].

Aside from the ability to scribble notes, it is possible to make {{Yonkoma}}, {{RPG}}s, and if skillful enough, small animations. It is even possible to set up [[AlternateRealityGame Alternate Reality Games]] given the ability to pass messages from person-to-person. You can also unlock various Stationery and features to use that can be purchased with the Nintendo 3DS's in-system currency Play Coins.

Perhaps most interesting of all is the popularity it has garnered not just from its messaging functions but from Swapnote's [[ExpositionFairy guide]] in the form of a VideoGame/{{Mii}} called Nikki (in the bottom left side of the pic to the right). Already various [[FanArt fanart]] of [[{{Meganekko}} her]] [[EnsembleDarkhorse have]] [[RuleThirtyFour popped-up]] since the app debuted. At New Year's Day at 2012, Nintendo themselves sent out a new stationery (that can be acquired by simply having a friend send a message with the new stationary to you), along with a QR Code of Nikki's own official Mii usable in Mii Maker.

To protect minors, Nintendo discontinued the application's [=SpotPass=] features on November 1, 2013, due to users sending each other offensive material.

Despite the end of ''Swapnote'', Nikki is still around: she's become the mascot for the news page of Nintendo's Japanese website, and starred in ''Nikki's Travel Quiz'', a trivia game about Japan that was exclusive to the Japanese Club Nintendo. She's also made appearances in other Nintendo software, having hosted a [=SpotPass=] art lesson in ''Art Academy'', been a Mystery Mushroom costume in ''VideoGame/SuperMarioMaker'', and received a set of badges to decorate 3DS home screens with in the ''VideoGame/NintendoBadgeArcade''. Plus one of the backer-designed enemies in ''VideoGame/{{Shantae}}: Half-Genie Hero'' is a Nikki homage called Ikki.

A new version of the program, ''Swapdoodle'', was released in 2016, that includes DownloadableContent and drawing lessons.

Has nothing to do with ''Manga/DeathNote''.

!! ''Swapnote'' provides examples of:
* {{Adorkable}}: Nikki. C'mon, look at her.
* DoubleUnlock: Once you unlock the ability to attach recordings to your notes, you still need to pay 10 Play Coins to actually use it. Thankfully this is easily earned by closing your [=3DS=] and walking around for about 5 minutes.
* ExpositionFairy: Nikki.
* MeaningfulName: ''Nikki'' is Japanese for journal/diary. ''Koukan nikki'' is a form of exchange journal among close friends.
* {{Meganekko}}: Nikki.
* {{Microtransactions}}: In ''Swapdoodle'', players can buy sets of stationary and art lessons.
* RolePlayingGame: [[http://www.youtube.com/watch?&v=YrDFhhh-MuQ This video]] provides an example of how to create a simple [[TabletopGames tabletop RPG]] within Swapnote.
* SpiritualSuccessor: To the DS's Pictochat.
* UnlockableContent: The ability to send pictures and sound attachments along with 3D writing are unlocked as you save/send more messages. Additional Stationery can be purchased via Play Coins.
* {{Yonkoma}}: You are given up to four pages for each message you send.
* VariableMix: The background music changes when reading, writing, or browsing your notes.
* VideogamePerversityPotential: You can send anything to anyone in your friends list. Even [[RuleThirtyFour that]], which ultimately contributed to the first program going offline.