Atmosphère is a CFW for hackable Nintendo Switch consoles, which include fusee-gelee vulnerable units and ipatched units running FW 4.1.0 for now although support for Switch firmwares up to version 7.0.1 will almost certainly come in the future.
Similar to other CFWs, Atmosphère lets you do a wide variety of things on your Switch including running homebrew games/utilities, using custom modules (similar to plugins in PSP/PSVita jargon), overclocking your console and even running a secondary version of Horizon OS stored on your SDCard via emuMMC.
Other than being quite feature-packed, this CFW is also frequently updated and a few hours ago, Atmosphère 0.9.3 landed with:

  • Significant optimisations, by hexkyz, to fusee’s boot sequence which means that Atmosphère’s boot times have been greatly reduced and you’ll be spending less time staring at its splash screen!
  • Automatic backing up of your Switch’s BIS keys which are instrumental in fixing a corrupted NAND especially on ipatched units since they don’t have the RCM bug
  • The “pm” (Process Manager), “creport” (Crash Report) and “fatal” system modules were rewritten with numerous improvements
  • The version string in the Settings App now displays whether you’re using emuMMC or not and defaults pertaining to hbloader’s memory usage in applet mode were added to ‘system_settings.ini’

  • The bundled version of hbl has been updated to version 2.2 (from 2.1) and hbmenu got updated to version 3.1 (from 3.0.1)
  • Other fixes and minor updates which can be found by browsing through its commit history

To grab Atmosphère 0.9.3, check out this link and make sure you update fusee-primary when installing it.