I've got a couple games that maybe fit this category.

• Kerbal Space Program. This had a sequel coming out that apparently wasn't going very well and was cancelled, so right now, the possibility of a complete additional game isn't that great. Spaceflight simulator, where one can design and craft spacecraft and amospheric craft, as well as space bases. One can fly to other planets, set up bases, set up satellite networks, etc. There are some "build your own vehicle"-type games, but not as much of a hard sim as this. I believe that X-Plane can handle atmospheric craft modeling, though the scope of that game is much smaller and it focuses more on flying the aircraft. Has a campaign to progress through, where one performs discoveries and conducts research. I'd recommend this to someone who hasn't played it and likes sim games.

• Kenshi. There's a sequel coming out, so maybe it won't be unique at some point. They player controls a squad that moves around the world in real-time -- there isn't an "overworld map". The squad can be split up into multiple squads. One can build outposts and defenses and such and have something of an automated economy. There's a tech tree. The world has various factions and dynamic control of regions, something like Mount & Blade: Warband. There are unique biomes to travel through. A fair bit of the world is placed. The world starts out in a mostly-hand-crafted, fixed state, but evolves over time. Character progression isn't based on point allocation, but on specific experience; have a character get hurt, and over time his ability to take damage will rise, and so forth. I think that this is still worth playing, though it's by no means a beautiful game and possibly (hopefully) will be surpassed by its sequel.

• Majesty: The Fantasy Kingdom Sim. A real-time colony sim that can mostly run itself. One has indirect control for the most part; one directly controls upgrades, certain spell and structure abilities, and can spend money to create "incentive flags" to create missions for characters to fulfill. I don't know if it's right to call it a single-game genre -- it's a colony sim, and other colony sims exist, like Rimworld, Dwarf Fortress, and such. Populus and some god games have direct control over spells. But I don't know of any other colony sim that plays much like it -- most of the focus is on upgrades and on countering waves of invaders, and the gold economy is ununusual. The same developer tried making a sequel, but eliminated the "sandbox" mode, and turned it into more of a puzzle game, and that game didn't do very well. One builds a colony in real time. There is no direct control over the individual characters, but for certain actions, one can spend money to incentivize them to do certain things. Characters level up and purchase equipment using gold they earn and that you expend on them to purchase items. Some of your control comes from things like building inns to cause them to spend idle time in particular locations. Building construction and maintenance is carried out automatically by peasants. As adventurers spend gold at buildings, it comes back to your control. I think that I'd have a hard time recommending today due to its age (you're going to have 2d pixel graphics that are going to be tiny on a current computer).

• Pinball Construction Set. This is a video pinball game where the player can use premade elements to easily put together their own pinball board. Very elderly now, dates back to the early 1980s. I remember being absolutely fascinated by this back in the day. Since that time, there have been many video pinball games, as well as some systems that permit some level of authoring capability (e.g. Visual Pinball can run user-created pinball boards), but these require a lot more effort and expertise and "real" authoring tools to put together a pinball board; one can't just drop in in-game and start throwing elements together. I don't think that I can recommend this, as it's absolutely ancient today.

• Noita. It's based on Liero, but really not at all like it. It's an action-roguelite (well, that's a genre, but nothing really similar beneath that level of specificity) that has side-scrolling over an open world. Various materials interact and have their interactions simulated at a per-pixel level, something like the "falling sand" genre. However, there are enemies running around, and the player controls a character that walks and floats through the world. One can find various containers of substances; one can try and mix things together to manipulate the world. One finds wands with spells; one can combine spells and various spell modifiers on wands to create all sorts of custom magic weapons that can range from utility to offensive. The aim, as with many many roguelites, is to try to use some luck and synergies between various items to come up with truly game-breaking combinations. I can definitely recommend this game; I found it to be very good value-for-money.

Honorable mention:

• Hostile Waters: Antaeus Rising. This is not a single-game genre, but there have only been two successful games in the genre, and one, Carrier Command, is from the 1980s (and which I've never played). You control a carrier (strictly speaking, an amphibious assault ship) that moves along an island chain; it can create surface, amphibious, land, and aircraft and weapons for these. One has a limited number of AIs that can control some vehicles automatically; one can give general orders to these, control the vehicles directly. One can capture more resources from the islands to expand one's abilities. There was a remake of Carrier Command, which flopped, and a sequel, Carrier Command 2, a relatively-recent game, but unlike Hostile Waters, is really intended to be played cooperative multiplayer; playing single-player places a very heavy workload on the player...so I have a hard time placing it in the same genre, even if it has many similarities and was inspired by the same game. While I enjoyed Hostile Waters and I think that it could still be enjoyed, it's getting a bit long-in-the-tooth graphically, and I recall it being a bit unstable even back in the day.