Depth is not the same thing as length
Most games recommended to Trimps players are simply long, and long is the easy part. What Trimps does is stack four reset layers that behave differently from each other: in-run equipment prestiges, the Portal and its perks, challenges that attach a rule to a portal, and then Universe 2, which is a second game with its own currency sharing your save. On top of that sits a real automation layer, map repeat settings and exit conditions you configure once and then live inside.
The result is a specific rhythm. You hit a wall, and the game does not tell you why. Somewhere among eight interlocking systems one is lagging, and finding it is the actual gameplay. Every number on screen is clickable and opens a breakdown of where it came from, which is Trimps quietly admitting this is what it wants from you.
So the test for anything on this page is not how many hours it holds. It is whether it gives you a diagnosis to make and a knob to turn afterwards.
Antimatter Dimensions
Antimatter Dimensions is the strongest pick and it is free here, built from Hevipelle's MIT-licensed source and served from our own domain with nothing phoning home. Around two hundred and fifty hours to its final Celestial.
It matches Trimps on the part that matters. Reset layers do not sit side by side, they sit on top of each other, and each one recontextualises what the previous layer was for: dimension boosts, then infinity, then eternity, then reality, at which point the thing you had been treating as the goal turns out to be a resource. Where Trimps hides the wall behind combat and logistics, Antimatter Dimensions hides it behind pure arithmetic. There is no army, no map, no equipment, no fiction at all. If a good half of what you liked about Trimps was the Trimps themselves, this will feel bare.
Its automation arrives later than Trimps' does and then goes further, ending in a scripting language you write your own reset conditions in.
Synergism
Synergism by Platonic is the other pure-numbers answer, free in the browser and MIT licensed, with five reset layers of its own and a Steam release. It is more arithmetical than Antimatter Dimensions and less elegant, in that its screens are dense with rates, corruptions and multipliers you are expected to hold in your head simultaneously.
Take it if the Trimps habit you enjoyed was auditing your own numbers. Skip it if you wanted the pushing-into-hostile-territory part, because there is none.
Kittens Game, which is deep in a different direction
Kittens Game will absorb you for the same number of months and it is fiddly in the same way, fifty-odd resources, thirty-odd buildings, a research tree measured in weeks, and a genuine need to keep notes. Free in the browser, paid on Steam and iOS, and its licence forbids anyone else hosting it, so we link out.
Be clear about the difference before you start it, though. Trimps only ever goes forward. A bad run costs you time and nothing else, and no number you have banked is ever taken away. Kittens Game takes things back. It runs a four-season calendar, catnip yields collapse in winter, and a village you grew too fast in autumn starves in front of you. The pressure is scarcity, not scale, and the skill it asks for is restraint rather than optimisation. Plenty of Trimps players find that annoying rather than interesting, and it is worth knowing which you are before you sink a fortnight into it.
Three more with the same appetite
NGU Idle, by 4G, is the game most often named alongside Trimps in these threads. Dozens of interlocking systems, gear, bosses, resets, and a deliberately ugly presentation with a funny voice underneath it. It earns the comparison on depth. One correction on the usual advice, including advice we gave here before we wrote the game up: it is free on Steam and it is Windows only there, and the browser copies people still recommend have gone stale. Kongregate no longer carries it at all, and the Armor Games build stopped receiving updates in 2019. If you want the game as it exists now, Steam is the only current version. There is also a separate guide on what makes NGU the kind of game it is, which is a different question from this page's.
Evolve Idle runs a civilisation from single cells upward and then resets the planet on several different terms, each one changing what the next run is allowed to do. That is the Trimps habit of rebuilding a plan around a new constraint, with a research tree wide enough to make it a real decision. Free in the browser, open source under MPL 2.0, and worth knowing before you start that it does not have offline progress in the usual sense: it banks time while closed and then spends it at double speed, which is a slower thing than it sounds.
Swarm Simulator is the clean, stripped version of the same appetite: a production chain of larvae into drones into everything above them, eleven tiers deep, heavy automation, and a number that does not stop. Much shorter than anything else on this page, free in the browser, and the only game here that is genuinely comfortable on a phone, which Trimps refuses to be.
What does not work, and why
Melvor Idle gets recommended to Trimps players constantly and it is the wrong shape. It is broad, it is enormous, and it has no prestige reset at all. Nothing compounds, nothing is recontextualised, and a skill you levelled is simply levelled forever. That is a real pleasure and it is the opposite of the one Trimps sells.
Progress Knight is a good game and a poor answer here. Its first life takes about seventy-five minutes, it holds two reset layers rather than four, and thirty to fifty hours covers everything in it. Play it on a weeknight, not as a replacement.
Clicker Heroes has one clean reset loop and a cash shop propping up the late game. Anyone arriving from Trimps will exhaust it in a weekend. The traffic runs the other way round, which is why the games like Clicker Heroes guide sends people here and this page does not send them there.
Where to start
Antimatter Dimensions, because it is free, it is hosted here, and its first two reset layers make the case inside an hour. NGU Idle if you specifically want combat and gear back, and you are on Windows.