Fool is a utility program which reboots a mainframe device for 1 turn, but also triggers a random daemon when used. It costs 0 PWR to use, and has a cooldown of 1 turn. Fool also has a passive effect which extends the durations of daemons by 1 turn.
Fool actually works as a targeted EMP effect, equivalent to the Subdermal Tools augment. This means that Fool destroys “EMP vulnerable” drones, disables Heart Monitors of Barrier Guards and OMNI Protectors, and breaks 2 firewalls instead if the target device has magnetic reinforcements and more than 2 firewalls. Note that these interactions are not mentioned in Fool's in-game text description.
Fool is a bad program. Do not be tricked into buying it just because it is cheap, thinking you can sell it later when you find a better program and you don't have to use it when triggering a daemon would be dangerous; it has a harmful passive effect which extends the durations of daemons, which applies whether or not you actually use the program. Some of the most harmful daemons — Labyrinth, Modulate and Paradox — have duration effects, so Fool makes them even more severe.
That said, in some specific builds, Fool can be usable. Rebooting a device for 0 PWR is a quite useful ability — you can loot Corporate Safes and other devices without hacking them, or you can use it to get past Security Cameras, Turrets or Laser Panels if you won't need to return back past them later. But triggering a random daemon is a significant downside; it is often preferable to just walk past a camera or through a Beam Emitter, taking one hit on the alarm tracker, the same as the weakest effect of Blowfish, rather than accept a random daemon which could be Validate or Labyrinth.
The downside of triggering a random daemon is moot when using Fool to reboot a device with an unknown daemon installed, which you would otherwise have to hack and trigger anyway; when the daemon is known but severe, a random daemon may even be preferable. Triggering a random daemon is also less dangerous when playing with the Contingency Plan DLC, which adds more less-harmful daemons to the pool.
Fool synergizes with Central's Antiviral Proxy augment, which turns Fool into a generator giving +5 PWR when used. Fool's passive effect can be mitigated with Bless, or by using Hunter or Taurus to trigger fewer daemons when hacking devices.