What kind of game this is
NGU stands for Number Go Up, and the game is not being coy about it. You start with a small pool of energy, a monster to hit, and a list of things energy can be poured into. Everything after that is the same act repeated at larger scales: find a new place to spend a resource, spend it, watch a number climb, unlock a system that produces a resource you did not have.
Structurally it is an idle RPG. Zones hold enemies, enemies drop equipment, equipment raises your power and toughness, and higher power lets you fight in zones you previously could not survive. Alongside the loot there are boosts, which are consumables that permanently level a piece of gear, so most of the mid game is a question of which items deserve your boosts before the next tier makes them obsolete.
What sits on top is the part people stay for. Energy and magic are capped, allocatable resources, and you spread them across NGU upgrades, Augments, Wandoos, the Time Machine and Blood Magic, each of which multiplies a different part of the economy on its own timer. Nothing is complicated in isolation. The game's difficulty is entirely a question of where your allocation should go this hour.
Rebirth
The reset here is Rebirth, and it is unusually gentle. Rebirthing restarts your progress through the zones and clears your accumulated energy and magic, but your permanent upgrade levels and your best equipment carry through. So a rebirth is not a loss, it is a rerun at a higher speed, and much of the skill in NGU is knowing that a run has stopped paying and cutting it short.
Two other structures sit around that. Difficulty modes escalate the entire game: Normal is followed by Evil and then Sadistic, each rebuilding the systems you already know with harsher numbers and new mechanics attached. Challenges, run as separate rebirths with a rule imposed, hand out permanent rewards for finishing them. The Infinite Tower of Pain and Suffering, universally called the ITOPOD, is the game's answer to what you do while waiting: an endless stack of floors your character grinds forever in the background.
Adventure mode, and the active half
The other half of NGU is not idle at all. Adventure mode is a side-scrolling combat screen with a hotbar, and bosses there are fought by cycling attack, block, parry, pierce and heal abilities in the right order against enemies that telegraph. It rewards attention in a way the rest of the game does not, and it is where the equipment you actually want comes from.
Titans are the checkpoints. Each is a boss with a stated power and toughness requirement, and each drops a set of gear that defines the next stretch of the game. The game is explicit that Titans keep working while you are away but that no items drop while you are offline, which is a fair summary of NGU's whole attitude: it will progress without you, but the good things need you present.
The humour
Every menu is a joke. The Steam system requirements list a sound card entry that reads "lol there's no audio at all" and finish with "Hi Dad". This is either a large part of the appeal or a reason to bounce off in ten minutes, and there is not much middle ground. It never lets up.
Where you can actually play it, which has changed
This is the fact most pages about NGU get wrong now. The game was a browser game first, on Kongregate and on Kartridge, and both of those routes are gone: the Kongregate listing now redirects to the site's homepage, and Kartridge no longer resolves at all.
A browser build does survive on Armor Games, and it still loads, but it is frozen. On 25 July 2019 the developer posted there that he would not be updating the Armor Games version any more, and the newest changelog entry on that page is Build .423 from 31 May 2019. Seven years of development are not in it. Treat it as a demo of a much older game.
The live version is the free Steam release, published on 1 October 2019, Windows only, free to play with optional purchases, with Steam Cloud saves and achievements. Steam's own minimum requirements list a broadband internet connection, so it is not something you can run on a plane.
There is no official phone version, and the Steam build is a desktop application, so a phone is not an option.
How long it takes
The thousand hours in this page's data is our judgement rather than a measured figure, and we found no HowLongToBeat entry to check it against. It is on the long end even by this genre's standards: the databases that categorise idle games by length put NGU in the years bracket, and players chasing the last achievements report totals well beyond anything a single sitting suggests. The first evening will show you maybe two of the systems described above.
Getting further
Rebirth early and often at the start. New players sit in a first run for days because it feels like progress. It is not.
Do not spread energy thinly. A few capped systems beat many half fed ones.
Do the Adventure mode bosses when you unlock them. Skipping the active half is the most common way to stall.
Who made it, and where to play
NGU Idle is by 4G, the solo developer who also made NGU Industries. Play it free on Steam, or try the frozen 2019 browser build on Armor Games if you cannot install anything.
The game is closed source and no licence permits anyone else to run a copy, so nothing on this site hosts one. If you want the same scale of progression in a browser tab, Trimps is the closest thing we list.