3DS:Flash Cards

The mostly questionable products passed as flashcards for the 3DS can be grouped as follows:

Vaporware
As early as September 2011, seemingly promising research by the Crown3DS team attempted to produce a viable gamecard emulation device, but nothing came out of it.

DS flashcards
After the R4 team disbanded, many DS flashcard clones came out that used suggestive and almost misleading names.

Updates
Nintendo continued trying to block them until the 7.0 update: anything supporting this 3DS version will work on any DS-compatible console known to date (unless it self-destructs as not rare with many bottom-barrel products).

Flashcard manufacturers such as the Acekard team provided firmware updates for their series of flashcards such as the Acekard 2i to work with the latest system firmware. At the end of 2012, no new available updates have been published, it is most likely that the team disbanded operations.

Some CFWs include patches to unlock any flashcard with a valid header (i.e. not the original autobooting DS/Lite only Slot-1 cards, like the R4) and even those can be used with a forwarder such as NTR Launcher or TWiLightMenu++.

Gateway
At the end of May 2013, the first commercial backup loader for the 3DS had been released: the Gateway 3DS, which much later was revealed to be a product of the post-sellout Team Xecuter (who also made the StarGate 3DS, the TrueBlue Mini, the Classic2Magic, and the SX modchips). Initially, the card was supposed to release at the end of July 2013, but pre-sales did not start until mid-July. The card was eventually available for purchase at the end of July.

The flashcard only supported firmwares from 4.1.0–8 up to 4.5.0–10 and could only hold one game on a microSD card. This restriction was later lifted with the release of v2.0 OMEGA, with its multi-ROM feature to hold up more than one ROM, including a selection menu.

The Gateway, however, is not technically a flashcard; rather, it's a novel accessory that fits into the gamecard slot (slot-1) and requires dedicated support for the OS; therefore, the Gateway requires the use of its dedicated and proprietary CFW, which has been criticized for including deliberate bricking code. The CFW lacked features compared to their competitors and was taking a long time to receive updates (the last version supported up to the 10.2 system firmware, however, it is possible to support later system firmwares by using unofficial patches). To their credit, the Gateway CFW introduced the first practical cheat engine and EmuNAND implementation for the 3DS.

Inside the package, you are provided with two cartridges: a blue card and a red card. The blue card is a rehashed R4/Ace3DS+ flashcard clone; these are very common to buy on marketplaces like AliExpress or eBay for $5 or more. This is used to play your DS-mode games as well as to install the exploit used to launch Gateway. The red card is for storing your 3DS games, which needs to be activated first with the exploit.

MSET Exploit
The MSET Exploit is an exploit found in the "System Settings" app on the Nintendo 3DS. The vulnerability was discovered by security researcher ichfly, sometime in 2012, and was later used by the Gateway 3DS. The exploit takes advantage of a flaw in the 'Nintendo DS Profile' settings, where an extremely long nickname or message would cause a stack overflow, therefore allowing the use of executing unsigned code.

The supplied exploit installer app that Gateway used was a modified version of ROP Loader by Fierce Waffle, adding their own logo and changing instances of ROP Installer 3DS to Gateway 3DS Installer. Sometime around 2015, support for installing the exploit on the New 3DS was added by Gateway.

This exploit was later fixed in system firmware version 7.0.0-13. This can be re-enabled, however, by installing an older version of the 'System Settings' app using FBI or GodMode9.

"Brickway" scandal
Gateway had a big monopoly position in the flashcard market, as many other manufacturers had hardly any of the features that Gateway had. During that time, numerous clones of the Gateway were made, such as the MT-Card, Orange 3DS, 3DS-Link, and R4i Gold 3DS Deluxe; curiously enough, even reputable brands later dabbled with this, namely the SuperCard DSTWO+ and the EZ-Flash Redux. Plus, they had also cloned Gateway's software to add their own features as well as their own logos. To discourage users from buying clone carts, Gateway had implemented code into the OMEGA v2.0b2 beta to detect whether the "Launcher.dat" file was tampered with. If a modification is detected, then the eMMC is locked with a password, rendering the system inoperable. However, if the SD card file-system was corrupted, then the same process can occur, resulting in unwanted bricks, even for legitimate Gateway owners.

Gateway's response was that they defended the fact that the firmware was free of any bugs and put the blame on users who were using clone carts instead of original Gateway carts. According to some users after confronting the team, Gateway had promised to replace defective consoles that their carts had bricked.

The scandal was so infamous that the community coined the term "Brickway", to criticise them for the vast majority of systems that they purposely bricked.

MT-Card
In late 2013, the MT-Card team launched the MT-Card, a clone of the Gateway 3DS. The team was, if not the first, to implement their own features into Gateway's code. Most clone manufacturers don't bother with adding their own features, other than to steal Gateway's launcher and add their own graphics. It was praised for its main selling point, which was to support multi-ROM games instead of one ROM, just two months before Gateway's v2.0 OMEGA beta. The FPGA can be upgraded with the use of a micro-USB cable and MT-Card's proprietary drivers and updater software.

Sky3DS
In late 2014, the first real-time flashcard for the 3DS was released, the Sky3DS (red button), which accurately ran clean dumps on unmodified consoles at the cost of not having a menu or modifying the console with an exploit, requiring the use of its button to cycle sequentially between ROMs. It also stores slot-1 saves in internal memory, which cannot be cleared and only supports 10 such games ever; tacky workarounds exist, but the ultimate solution for this non-updateable card was to sell a blue-button model without this restriction.

But both models are incompatible with most 9.6+ titles using 0x1FE protection; this limitation too received both a workaround (editing the ROM, which breaks its signature and therefore requires a CFW to allow it again in the first place) and a new flashcard, the orange-button Sky3DS Plus, which also added a backwards-cycling button and dropped the requirement for the proprietary PC software in favor of taking clean ROMs and a configuration file on a standard filesystem.

Stargate
By the end of 2017, the Gateway team (launched under false name) a new product, the Stargate 3DS, effectively combining a DS and 3DS flashcard: its two buttons can be used to cycle between 3DS ROMs like on a Sky3DS+, but if pressed simultaneously, the card switches to operating as a DS flashcard, which, being almost intrinsically capable of running homebrew, includes in its kernel/menu the ability to directly select a 3DS title.

Unfortunately for the team, this premium product was too little (except in price) and too late, as CFWs with patches giving near total freedom in unsigned title installation and operation were already generally appreciated as superior, and both sighax and ntrboot were released in that summer, ultimately giving the ability to cleanly load CFW regardless of system version.