Something has landed on the Moon.

A huge alien mothership sits on its near side, and every month it launches a fleet at Earth. Its target is the Command Nexus, the last command centre on the planet. Hold it for one year.

Perimeter Zero is a tower defense game drawn in glowing neon line art. Every building needs its own cables, every tower needs power and ammo, and every enemy wreck is scrap your drones have to go and collect.

HOW IT PLAYS

Each month has two turns:

• Build Turn: spend Iron on towers, generators and support buildings, then run underground cables between their ports. Take your time.
• Attack Turn: call the wave in. Ships launch from the mothership, boost across space and dive onto your base, landing anywhere between the Nexus and your outermost building. Your towers fire on their own, so what you built has to work. Waves are big, and battles are long enough to watch your plan hold, or fail.

Survive twelve months to win.

WHAT MAKES IT DIFFERENT

• You wire everything. A building doesn't work until its cables do, and every port holds exactly one cable. Towers need a power cable and an ammo cable to a powered Ammo Depot.
• A live power grid. Generators make Power every second, from the small Solar Panel up to a 10 Power/s Nuclear Reactor, and every building draws it to run, in the Build Turn and the battle alike, so the grid you build is the grid that fights. Hover any building to read its hull, its power and ammo state and what it is cabled to. For a generator, the hover also shows how much its grid has left. Click a generator to pin it, light up its cables and see exactly what it is holding up. You can also cut it loose with one button, if you want to find out the hard way. The Nexus makes only a trickle, so your first job is a Solar Panel or a Wind Turbine. Each cable network balances on its own. If a network draws more than it makes, Battery Banks cover the gap. When they run dry, the buildings farthest from a power source shut down first. A grid that is committed past its output shows a warning over its station before you call the wave.
• Scrap you have to collect. Destroyed ships break into glowing wreckage that falls to the ground. Your Salvage Depot's drones fly out to collect it, but enemies shoot at them, so they wait until it's safe.
• Drones that repair. A Repair Bay sends drones to fix damaged buildings between hits.
• A roster of ten enemy types, each with its own weapon and target:
  • Interceptors: fast and fragile, firing tracer bursts.
  • Breachers: go after your utility buildings.
  • Gunships: the steady damage.
  • EMP Corsairs: ignore your towers and hunt your power grid.
  • Drone Wings: swarms of ten.
  • Shield Carriers: protect their escorts.
  • Dreadnoughts: lob siege shells from long range.
  • Hive Pods: burst into three Splinter Pods when they die, so splash damage makes more targets.
  • Broodships: keep launching Drone Wings until you kill them.
• Shields that visibly work. A Shield Projector's dome and a Shield Carrier's bubble stop shots at their edge and dent inward where they are hit. A Carrier covers every escort with any part of its hull inside, and shots at a ship land wherever they touch its hull.
• A Nexus that fights back. From the first wave the Command Nexus can burn a line through a formation with Lance Strike. Upgrade it for Ion Storm, a field that grinds and staggers everything inside, and Solar Lance, a beam you sweep by hand for as long as its stored Power lasts.
• Zoom from your base out to the Moon in one continuous camera. Watch each wave leave the mothership and follow it all the way down.
• A finale worth surviving for.

GAME MODES

• Tutorial: a guided first month that teaches every system one step at a time, from placing your first tower to cabling power and ammo to surviving a wave.
• Normal: start with a working base already built and cabled: two Pulse Sentries, an Ammo Depot, a Repair Bay, a Salvage Depot, a Wind Turbine and a Solar Panel.
• Hard: start with only the Nexus -- a trickle of power and 50 in reserve for its weapon -- and build everything yourself.
• Sandbox: unlimited Iron, wind the month back and forth with [ and ], and build the next wave by hand — pick exactly how many of each ship turns up, or summon the mothership outright. Everything else plays by the real rules, so you can throw anything at a layout the moment you have built it.

Two more difficulties were made for the game jams this build was entered into, and both drop you at the end of the campaign instead of the start:

• Imminent Doom (Godot Wild Jam #97 — theme: Imminent Doom): Month 12 of twelve. One Build Turn, 5,000 Iron and an empty ring, then the last wave, the finale and the mothership, back to back. Everything you spend it on is everything you will have.
• Immortal Boss (Mini Jam #59 — theme: Immortal): start inside the mothership fight with 3,000 Iron. This is the one difficulty where the build tools stay live through the battle — place, cable, move, dismantle and upgrade while the hull is shooting at you, and pay for it with the scrap your kills leave on the ground.

FEATURES

• 16 buildings: 6 towers, 5 power buildings (up to a 10 Power/s Nuclear Reactor) and 5 support buildings
• A Command Nexus weapon you aim yourself from the first wave, with two more to unlock and a selector to choose between them. Hover an ability for its damage and cost. Every tower is available from the start.
• A twelve-month campaign that ends in a boss fight against a 1,200 m mothership
• A guided tutorial you can walk out of at any point and keep the base you built
• A report after every wave: what it cost and paid, and every building you lost -- where it stood and what killed it; click one to fly there
• Save and load, with 10 slots plus an autosave at the start of every Build Turn, and F5 to quicksave. Saving during a battle keeps the Build Turn before the wave, and tells you so.
• A pause button on the speed bar that stops the battle but not you: pan, zoom and inspect while it is frozen
• Game speed ×0.5 to ×10, remembered separately for building and battle
• An opening cinematic and a victory finale, both skippable
• Sound effects and ambient background loops, with separate volume controls (a new soundtrack and effects are coming in 1.0)
• A smooth camera: panning eases in and out, and Home glides back to the base
• Menus built from the same panels as the in-game HUD, and a tabbed settings screen (Graphics, Audio, Display, Gameplay, Controls)
• Fully rebindable controls, a UI scale setting for the HUD and menus, a warning (and an error icon on the grid) if you call a wave with a power grid that will draw more than it makes, and an optional one for buildings with no power or ammo
• A build bar that shows every building as its own line art, with its cost, its power draw and what it does on hover
• Graphics presets from Potato to High, built to run smoothly on older integrated graphics
• CONTINUE on the main menu, straight back into your last Build Turn
• Two game-jam difficulties, with a screen on first launch that names each jam's theme and what this build has for it

CONTROLS

Every building and every tool is on the bar along the bottom of the screen — click it, or use the key. All sixteen buildings are always visible; TAB only moves which page the number keys drive.

Action	Key	Mouse
Zoom	—	Mouse wheel
Move camera	WASD / arrow keys (also brings you back from the Moon view)	Middle-mouse drag
Centre on the base	Home	—
Quicksave (in a battle it keeps the Build Turn before the wave)	F5	Pause → Save Game
Pick a building	5–0, − (TAB cycles the keys through DEFENCE, POWER and SUPPORT)	Click its tile
See what a building does	—	Hover its tile
Upgrade the Nexus	U	Click the U button
Pick / arm / fire a Nexus ability	Q arms the picked one, then click (hold to sweep the Solar Lance); Q again cancels	Click a chip on the ability panel to pick it
Power cable / ammo cable	E / R	Click the E / R buttons
Move / dismantle a building	M / X	Click the M / X buttons
Flip facing	F	—
Call the wave	Enter / Space (asks twice if a grid is short of Power)	—
Pause / resume	— (bind one in Settings > CONTROLS)	Click the pause chip at the left of the speed bar
Build during the fight (Immortal Boss only)	the same keys as a Build Turn	the same bar
Change month (Sandbox only)	[ / ]	—
Game speed	` 1 2 3 4 = x0.5 x1 x2 x3 x4	Click a chip (x10 is mouse-only)
Show a tower's range	—	Hover it, click to pin
Inspect any building	—	Hover it, click to pin
Disconnect a power station or Ammo Depot	Del	Click DISCONNECT (asks once)
Jump to a problem building	—	Click the warning pill
Spawn the mothership (Sandbox only)	G	Click SPAWN MOTHERSHIP
Fullscreen / windowed	F11	—
Settings	P	—
Pause / back	Esc	—
Pause on the INFO screen	Esc	—