Here is the full list of all 42 Gunpoint achievements. It takes around 6-8 hours to unlock all of the achievements on Windows.
Defeat Gessler by rewiring his gun.
Create a custom mission with at least one objective.
Use the Longshot to make a guard unintentionally shoot another (outside of the test lab).
Use the Prankspasm to knock out someone who isn't standing near a power socket (outside of the test lab).
Chicken out of telling Katie the truth at the last minute.
Slam Fritz Gessler's office door into him.
Upgrade your battery capacity to the non-figurative max.
Knock Fritz Gessler out of his office window.
Notice the story doesn't necessarily gel with the mechanics. Become qualified games journalist.
Intimidate Fritz Gessler into surrendering.
Beat Fritz Gessler to death.
Knock Fritz Gessler out with a punch.
Mock the chief of police at a critical moment.
Complete a mission that has guards with no violence, witnesses or loud noises.
Kick Fritz Gessler's office door into him.
Free an innocent man at the expense of catching a guilty one.
Complete the police chief's missions without incriminating yourself.
Voluntarily tell Katie the truth.
Steal Gessler's technology for Rooke.
Use no violence at all on a mission that has guards.
Publish your personalised epilogue.
Complete the game.
Shoot Fritz Gessler.
Catch a guilty man at the expense of freeing an innocent one.
Use the Gatecrashers to kick a door through a window.
Use the Gatecrashers to kick a door into a guard.
Use the Gatecrashers to kick a door off its hinges.
Help justify my early, not entirely wise choice of game name by holding someone at gunpoint with the Resolver.
Upgrade your Bullfrog Hypertrousers to maximum jump strength.
Complete a mission faster than I can.
Knock a guard out by opening a door into him.
Conceal your presence at the DataSec break-in from Mayfield.
Upgrade your Bullfrog Hypertrousers to pounce instantly.
Tell Gessler that Rooke's hired you to betray him.
Use the Hushcracker to jump through a window silently (outside of the test lab).
Get knocked down by an opening door.
Leave no living witnesses to your presence on a mission that has guards.
Use the Crosslink to create an infinite loop that burns itself out.
Jump into an Enforcer to knock him through a window.
Use the Dropshot to land silently from a great height.
Wire an elevator button to trigger something when the elevator arrives.
This is an achievement in name only. No-one admires you for punching a guy that many times.