MegaBooster
Click on a dynamic object and attach a booster to it or just click on the ground to put one upright. Rocket gimble attempts to maintain the orientation when attached, so if you put flat on the ground then it will try to stay upright. attaching the engine to something sideways will cause the rocket to gimble and attempt to maintain that direction. Other keys/options on the bottom left of the screen in game.
To turn on realistic flames for perfect video or screenshots, go into the option (O) in game and turn them on. Performance will goes down, but aesthetics goes brrrrrr.
This mod is an overkill version of the basic booster. You can adjust the thruster strength and uses a gimbal control to maintain attitude. When realistic flame effects are on, a pressure field is simulated to give more realistic fire effects. Press (F11) to see the pressure field in the engine bell.