(Note that this is still being worked on, and this is basically a heavy adaption of zoogie's "A Pretty Brief History of the 3ds Hacking/Homebrew Scene" from the "3DS hacking scene history" section on GBAtemp)
2011
March
March marks an important date, the release of the Nintendo 3DS in the west, and the creation of 3dbrew.
June
Not sure about info (come back to later)
September
Crown3DS teases a promising video of a flashcard, but instead we got an Engrish website promising the community that they are progressing.
December
Release of tools that convert video to stereographic 3D video that is compatible with the 3DS photo app (maybe paraphrase and look into this more)
2012
Unknown Month
Believed that Neimod's hardware RAM dumps and internal research lead to the first userland and a9 exploits.[1]
March
The first (?) homebrew written in .cxi format, being "Hello World" written by Xcution (auther of CiTRUS,
2013
August
August of 2013 is a pretty important year of the 3DS community, as it is when Gateway-3DS released, being the entirety of homebrew in the early years. At this time, there was basic arm9 homebrew possible via an MSET exploit combined with p3ds, [1] which are python tools for the 3DS.
December
Users in the community figure out how to reverse engineered the Gateway-3DS payload to create their own NAND emulation (or redirecting). Specifically users Smealum and Yellows8 create a private payload called RedNAND.
2014
January
brickgate/brickway - A scandal where Gateway releases a FIRM that intentionally bricks 3DS's that run their software on Gateway clones such as R4 and Orange3DS.
March
The first commit of Citra [2] is released.
November
The leak of Palantine [3](cfw made by Yellows8 and other) occurred, bringing a closed source custom firmware to the public (with limitations such as the EmuNAND not being update-able, a low-boot rate, not fun to install, etc. What it did do was run cias, which caused Gateway to add this feature as well.)
The release of Sky3DS (could play clean cart roms, but no homebrew yet.)
The release of the userland exploit ninjhax [4].
2015
January
Gateway cracks 9.2 and updates their flashcards to OMEGA. User yifanlu posts a blog about reverse engineering memchunkhax/firmlaunchhax combo used by Gateway, and teams such SALT, roxas75, and patois implement quickly.
February
The release of roxas75's rxTools.
May
The release of Pasta CFW (namesake coming from the leak of sigpatches of pastebin). It combined the works of patois' Brahma (open source memchunkhax/firmlaunchhax) to make the first open source custom firmware (no emunand).
Rxtools is patched out with signatures made by ahp_person (appletinivi), and Roxas does not like this
June
Roxas eventually gives in, releasing the rxTools source and adding the sig patches in officially, then quits the scene.
(Maybe add on)
July
The release of Ninjhax2x.
August
The release of Tubehax, a primary userland exploit that took advantage of the 3DS YouTube app, unfortunately being patched a couple months later on all firmware.
The release of Ironhax, the first secondary userland exploit (this means that it requires a primary, like Tubehax, to install).
The release of Reinand, the first full featured New3DS custom firmware.
September
The release of Menuhax, a secondary home menu exploit which allows boot time userland execution (maybe change up wording, very very close to original).
The release of Browserhax, which are primary exploits that used the browser for the N3DS and O3DS that would be updated every so often in the coming months.
December
Sky3ds+ released. bypassing cart-based AP in recent games and adds a filesystem-based game loading feature among others.
The CCC hosts 32c3 in Hamburg, Germany, where snshax, arm9loaderhax, memchunkhax2, and ntrcardhax are revealed. The userland exploits Menuhax and Ironhax (not sure whether to put Ironfall or hax as it is typed out as Ironfall on gbatemp page used for most, if not all of this) are updated as well.