BoosterGuidance will autonomously guide a Booster to land on a drone ship or the launch site (or anywhere else) using a combination of Boostback, Re-entry Burn, Aerodynamic Descent and Landing Burn, i.e. SpaceX Falcon 9 style. Select your landing point either by clicking on it, typing the latitude+longitude+altitude or selecting a target (e.g. drone ship). Its aimed to be reliable and fairly easy to use. I've also made it work in Realism Overhaul where limited throttle able engines and limited ignitions mean you can't play fast and lose with your engines. With suitable engines and using the right number active you can achieve this is Realism Overhaul which gives a real feeling of satisfaction.

The mod relies on accurately simulating the entire trajectory to landing including burns later in the flight which means guidance should be accurate without the need for any heroic manoeuvres as the impact of say the reentry burn is properly factored in. BoosterGuidance will continuously monitor the target error and aim to reduce it in boostback, re-entry burn, aerodynamic descent and in the landing burn steering either via engines or via grid-fins depending on the phase of flight. You can set the steering gains during the flight to give the grid fins more/less to do, and configure the reentry burn via altitude and target velocity. Some more advanced settings allow you to set safety margins, speed of final descent, at what height to give up steering and more. You can also log the whole flight and plot it to examine in detail what happened and how closely you could copy SpaceX.

Here's some videos showing it working with a single stage Falcon 9 booster

Falcon 9 Return to Launch Site Video

In Realism Overhaul with a 2-stage Falcon 9 rocket where I make a half-hearted attempt to get the 2nd-stage to orbit.

Falcon 9 2-stage Return to Launch Site in Realism Overhaul Video

This mod is very usable and lots of fun now but has a few limitations I'm working on.

Clicking the target only works close to the terrain or there are physical structure (some KSP/Unity Raycast limitation I don't understand)

In Realism Overhaul you may need to manually reduce the gain close to landing to avoid large oscillations

Landing legs deployment is unreliable

Guiding more than one booster simultaneously should be possible but is currently unreliable. My goal is a Falcon Heavy two booster landing. That will be awesome!

It should work on other planets too though the trajectory should be sub-orbital to impact the ground within about 10 minutes as simulation time is limited for CPU reasons