The following are system-web-browser exploits for Nintendo 3DS, the ones hosted here are for booting the *hax payloads. On a supported browser, you can go here, which will automatically determine which exploit to return for your browser.
Once you boot into the payload successfully, you can then install exploit(s) from here(this is highly recommended). This highly recommended because of the browser-version-check implemented with v9.9, see here for details.

The following QR-code can be scanned by an Old3DS/New3DS from the Home Menu camera menu(if the QR-code menu option is available), for accessing the auto page:

Regarding source repos, the common codebase is located here, and the source of this site is located here. See below for the exploit repos.

Note that systems where the system was updated with a >=v9.9 gamecard sysupdate have a dummy browser installed, unless an online sysupdate was done afterwards. See here for details. The system-version for this is 9.9.0-X, where X is less than 26.

The only required SD-card setup is that you extract the homebrew starter-kit on SD.

Before using any of the Old3DS browser exploits, you should do the following:
  1. Use the browser 'Initialize savedata' option.
  2. Enter the browser again so that savedata can be setup. Then goto directly to the exploit page(this can be the auto page), you can return to Home Menu for scanning the above QR-code for this if you prefer.
  3. Exit the browser so that the current page automatically loads when the browser gets launched again. At this point the only pages in the browser history should be the default 3ds-bookmarks page followed by just the exploit page.
  4. Enter the browser then trigger the haxx as described in the repos linked below(when they don't auto-trigger).

As of March 24, 2016, the browser-version-check requires that the installed Old3DS/New3DS browser be on >=10.7.0-32. This does not apply for New3DS v10.2. To bypass this requirement on Old3DS/New3DS(this bypass is only usable prior to 10.7.0-32 since it's fixed with 10.7.0-32), you can do the following(if you want to know how this works see here):
  1. Goto System Settings. Then change the datetime to January 1, 2000, 00:00.
  2. Use the browser 'Initialize savedata' option, before any page gets loaded triggering the browser-version message.
  3. Continue to use browserhax as normal.
  4. Note that you must not press the HOME button to return from the browser normally, otherwise you will have to reinitialize the savedata again. Once the datetime reaches January 2, you will have to repeat these steps if you want to continue using this bypass.

Due to the *hax payloads, the exploits hosted here are only usable on systems with system-version >=v9.0 with the system web-browser installed.

Using the auto page(such as with the above QR-code) instead of going to the exploit pages linked below manually, is highly recommended.

If any crash/hang ever occurs, you will just have to run the exploit again, with a hardware reboot if this occurs after the initial gray-screen color-fill. See here regarding crashes/hangs/screen-colors.

The exploits marked 'obsolete' are not returned by the auto-page since better exploits support the same versions the obsolete ones did.

System Exploit Supported system-versions Fixed with system-version Returned by the auto-page Exploit runs automatically Repo
Old3DSsliderhax (obsolete)'All' <=10.1.0-27(aka <=X.X.X-27)>=10.2.0-28(aka >=X.X.X-28)No, obsolete.No, see repo.Here
New3DS3dswebkithax_removewinframe (obsolete)All <=9.8.0-25(aka <=X.X.X-25)>=9.9.0-26(aka >=X.X.X-26)No, obsolete.YesHere
New3DSbrowserhax_frightAll <=10.1.0-27(aka <=X.X.X-27)>=10.2.0-28(aka >=X.X.X-28)Only when the browser version is supported by this exploit.YesHere
New3DSbrowserhax_fright_tx3gAll <=10.5.0-30(aka <=X.X.X-30)>=10.6.0-31(aka >=X.X.X-31)Only when the browser version isn't supported by older exploit(s).YesHere
Old3DSspider28haxOnly 10.2.0-28-10.5.0-30(aka X.X.X-28-X.X.X-30)>=10.6.0-31(aka >=X.X.X-31)Only when the browser version is supported by this exploit.YesHere
Old3DSspider31haxOnly 10.6.0-31-11.0.0-33(aka X.X.X-31-X.X.X-33) and X.X.X-2 - X.X.X-27>=11.1.0-34(aka >=X.X.X-34)Only when the browser version isn't supported by spider28hax.YesHere
New3DSskater31haxAll <=11.0.0-33(aka <=X.X.X-33)>=11.1.0-34(aka >=X.X.X-34)Only when the browser version isn't supported by older exploit(s).YesHere