You might actually want to look for RPG systems that are a particular kind of bad.

Some systems with decent math behind them fail because they are too fiddly. They might have tons of modifiers to track, cumbersome rolling, lots of traits based on averages of other traits, and so on. Those types of systems can often be great for things like MUDs, because the computer can hide most of it from the player. And, maybe a roll takes 10 times as long, but that just means the software can do it in 10ms instead of 1ms, so who will care?

If Earthdawn was open licensed, I’d suggest it as being “the right kind of bad”. It’s weird exploding pool step system is interesting because the dice for each step are set up such that the average roll of the pool is approximately the step number.

I’m not an expert with it but the basics of Traveller/Cepheus seemed pretty straightforward. Roll six-sided dice and add the appropriate modifiers.

• Encourage solo exploration and survival.
• Have distant sci-fi, cyberpunk, and dystopian themes.
• In addition to equipment, implant, and class bonuses, will incorporate gunplay.

Maybe check out Mutant: Year Zero? AFAIK Year Zero engine plays well with survival and resources. Might be a little bit too light for computer GM, though.

You can find SRD of the base system in the middle of the text here

Try looking at Shadow Run's ruleset. It might get you started with gunplay, the themes, and class stuff (idk about implants I've never played it myself). Also Fantasy Flight Games has a pretty maleable ruleset, but its chunky and might be a bit much to parse through. But a lot of systems are built on and with FFG rulesets.

You might want to look at some of the open source RPG rulesets out there to get a sense for what there is. That'll help you come up with a set of internal rules (i.e., how the MUD actually implements game mechanics) for your game engine.

Two possible mechanics that just came to mind would be Nd6 (roll some number of d6) (which goes all the way back to Illuminati by SJG) and blackjack style (closest to some difficulty without going over) (Eclipse Phase implements this with d100, and leaves a lot of wiggle room for modifiers).

A great way to develop the most user friendly ruleset is to have them compete! Here's what I mean by this: once you have your top 5ish systems, just lookup 1 vs 2, 1 vs 3, and so on. You'll notice some rules that are coming up almost every time. These are the greatest pain points for users of that ruleset. From here, you can cherry pick the best of all worlds! A word of caution: if you intend to avoid a particular rule or style, consider why it exists in the first place. Often when a system keeps a part of the game most players dislike it's because that system is essential for maintaining balance somewhere.

If you want crunch -> Aftermath! from Fantasy Games Unlimited. You can get a copy here.