I was thinking about how to create a less-violent RPG. The heart of the RPG setting - the violent murder of as many locals as possible - has always been both nonsensical and lazy. So I'm always thinking about ways to make RPGs that are not about murdering locals.
The core problem is that the combat engine in an RPG is basically the "wheels" of the "car". All the exploration, leveling, gaining and losing party members, looting, attrition, buying and selling, all that stuff is all oriented around the battle system. The battle system is, in turn, built with enough statistical dependencies to allow for those other play systems to link in and affect them.
So you can replace the combat engine of an RPG, sure. But the initial impulse is to replace it with a minigame.
Minigames serve a different purpose. They are generally more skill-based than statistical, and their outcome is generally binary. Minigames are essentially gating systems, while RPG battles are essentially grinding systems. They're very different, even if at first glance they seem to have the same basic role.
The good news is that if you realize the difference, you should be able to build a replacement. So now that we've established that, let's talk about Taiga Repair, Construction, and Terraforming.
Taiga RCT is an interstellar contracting company that goes from planet to planet building and repairing things. This is a very similar theme to the idea of an adventuring party that travels from town to town. Except, instead of murdering wildlife, these adventurers repair, construct, and terraform. Imagine it's just like a classic RPG - lots of exploration, side quests, talking to people, buying and selling weapons... except that the theme is high-tech construction.
So as you wander around a subterranean base, you'd have a "random encounter" with, say, a malfunctioning door, or perhaps a clogged ventilation duct, or maybe both. Sound lame? More lame than bats and rats and slimes? Those are the equivalent enemies. Later on you'll be trying to construct giant bridges, desperately trying to get the pumping system on-line so you can prevent the undersea city from flooding before lowering the bulkheads, fighting back a crop blight while trying to increase the amount of oxygen in the air, and so on.
The combat in the game is fundamentally similar to the combat in any RPG - except that you're fixing malfunctions or constructing systems rather than killing monsters.
Every character has health, except that in this case it's self-confidence. Systems which continue to malfunction even when you're trying to fix them cause you to lose self-confidence, while repairing or constructing functional systems gives you some back. The party as a whole also has a level of confidence - the confidence the locals have that they'll be able to fix things. This allows you to gate things like advanced equipment, tiered quests, and so on based on what the locals think the party can handle.
Resolving these challenges is similar to a combat RPG as well, in that you have a "basic attack" which attempts to repair or construct, as well as more constrained techniques to buff, debuff, heal, multi-attack, and so on. However, there are a few key differences.
The first is that the enemies you face are not enemies, they are systems. But the malfunctions and missing pieces are not necessarily standalone, and they are frequently related to other malfunctions or missing pieces. You encounter a broken automatic door. It's possible for you to fix it by just brute-force attacking it, but you'll probably lose a lot of confidence, because you're essentially rebuilding the whole door from the ground up.
On the other hand, you can dig deeper and reveal that the broken automatic door is because of the broken sensor system above the door - you've added another enemy to the fray, but it's a much weaker target that will fix or severely weaken the door glitch once repaired. You can dig deeper yet, if you like, revealing that the broken sensor is because the ventilation system has bad filters, and spews dust everywhere - including on to sensors.
These can be quite complex, with several challenges linking to the same base error, or with several errors fueling a single fault, or even with circular fault chains... that can make encountering the same "enemies" still quite unique-feeling as their interconnections are always different.
This brings us to the next point. The challenges can be random, but they are constructive rather than fire-and-forget. Because of this, there is interconnectivity between the battles in the form of fundamental systems. In the case of a subterranean base, the fundamental systems might include the life support system and the power supply. In the case of a crop disease terraforming situation, the fundamental systems might include the crops and the atmosphere. If you're building a bridge, the fundamental system is the bridge you haven't finished building. In all cases, the defects and deficits in the fundamental systems can be steadily addressed by solving individual battles.
While you don't have to use every battle as an opportunity to gnaw away at these fundamental systems, if you feel up to it you can do so by simply digging until you encounter a cause that is part of the fundamental system. These are much more difficult enemies than the surface-layer stuff, so you want to be careful. For example, it may be significantly better to simply repair the door sensor than to try to fix the busted filters, because the busted filters are very difficult in comparison. But if you fix the busted filters, you'll get a boost to what the people on the planet think of you, and the fundamental system will be slightly closer to being completed/repaired.
This approach allows us to create random "dungeons" and turn the game into a randomized adventure. Every "dungeon" is a facility that has a few fundamental systems that are deficient, and then there's a bevy of surface malfunctions that can be traced back to that. Often you'll need the locals' help - after gnawing on the fundamental system for a while, it'll level up and things will become more difficult, so you'll need to find the designer or the implementer or someone with lots of experience to help you lower the difficulty back down to manageable levels.
This also allows us to have a lot of different kinds of societies with a lot of different preferences, something that is sorely lacking in today's RPGs. Because every society of every kind has facilities, you can represent a specific society's culture and needs and preferences by what kinds of facilities they have with what kinds of subsystems. Similarly, the equipment you buy locally will always be the strongest because it's the equipment designed specifically to work with the local systems. Equipment from somewhere else isn't as perfectly tuned to this tech.
There can be a class-based party system just like any other RPG. Except that instead of warriors and mages and rogues, you'd have engineers and mechanics and researchers.