flog is a hidden NES emulator included in every Switch console, except those past system version v4.0.0.
flog, golf backwards, can only officially play one game: Golf, which is embedded into the emulator's binary.
This is a tribute to Satoru Iwata, and as such to run the emulator your Switch's month and day must be July 11th, the date of Iwata's passing, and then on the home screen you must perform Iwata's Direct gesture. If your Switch has ever connected to the internet, or was updated past system version 1.0.0, you'll have to wait for the actual day, manually setting the date to July 11th will not allow you to run flog.
However, it was removed in v4.0.0, and overwritten with junk data.