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