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