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