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