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