Kerbal Space Program

As far as I understand it, the SAS's PID controller constants are now fixed and thus in most cases out of tune with th ship's response.

In small and light ships, or medium-sized ships with lots of RCS thrusters ( and empty tanks), SAS overshoots so badly, that it sometimes never stabilizes.
And when the ship is only slightly wobbly ( large ships, or anything with a docking port naturally are ) ASAS+RCS action will almost always cause undamped oscillations, that, even when they don't break the ship apart, make ASAS+RCS all but useless.

All this could be solved by allowing the user to do some loop tuning on the PID constants by clicking on ASAS would display GUI window where you could, within certain limits, change the PID constants.

For example you could reduce the overall force to prevent the ship from overshooting hugely when it spent fuel, decoupled stuff, etc... and is now much lighter as it was initially. Or to bring the response time out of tune with ship's wobble resonance frequency so that it can dampen out oscillations instead of creating and amplifying them.