REM Overhaul 9.0.0 - for game's version 9.x+
https://www.nexusmods.com/x4foundations/mods/848
What is REM Overhaul 9
With version 9.00 I had to cope with the changes introduced by Egosoft, so the mod went through many changes.
First of all, unfortunately, ALL added REBIRTH SHIPS are removed. They got broken by the game's update.
REM 9 goes back to its root. This mod is meant for player wanting a true hard-core, real physics game. I went back to the concept of my old Rebirth Physics Mod but with a problem: in Rebirth, player ships is unique, you can make it behave in a very realistic way while the (stupid) AI has easier physics. In X4 it is a pain to find a fine compromise for all the ships.
This is not a "rebalance this or that", this mod drastically changes the behavior of ships in the game turning it into an experience more similar to classic simulation games, such as the recent In The Black or Elite Dangerous (partially).
Ships receive a realistic engine's and thruster's push and every movement is "heavy", you feel it (some effects are also added).
Secondly, REM keeps its traditional RACE/CLASS-specific equipment. With 9.00 Egosoft went even more deep into the idea of universal equipment for all ships which, to me, makes no sense. The lego-like idea behind this is frustrating if you enjoyed older X games where every ship had its dedicated equipment and felt unique. For a better gameplay, every race also produces some special equipment that is sold to all other races and is fitting to any ship. Teladi, as per tradition, are particularly open to other races. Their equipment is also used by pirates. Pirate ships have this unique feature: they can mount everything...they need to.
REM 9 has a big change in how travel drive works. While assisted speed is similar to vanilla (but accelerations are realistic), when using travel drive every ship can remove the speed cap (there is no limit in space except the speed of light). But travel drive is not the "magic tunnel" where you instantly accelerate to insane speeds. Acceleration is not different from that of the booster. Ships will accelerate slowly and even if they have ideally no cap to the travel speed, they will never go so far (you can if you want).
Travel speed is a kind of flight assist off (for all ships) and has peculiar physics. At lower speeds (which are what the ships will always use, within about 8000 m/s, there is no added friction (there is no friction is space) and inertia is still relevant. At higher speeds the ship will become hard to maneuver and to turn but inertia is removed or too many weird things happen

.
REM 9 also keeps the general rebalancing that emulates the older X2/X3: capital ships are very strong (and costly), medium ships are stronger and specialized, so on.
Weapons in the version B of the mod are lethal (high speeds and range) but XL/L/M ships are much stronger than vanilla.
Mod indeed comes in 2 flavours:
Mod A - vanillesque experience, ships have an assisted speed cap similar to vanilla (but realisit accelerations)
Mod B - hardcore experience, ships have a very high cap but booster is not so powerful, is used as afterburner
For now only VERSION A is available
List of features:
- reworked physics for all ships according to "realism", acceleration is the differentiating factor (version A and B)
- unlimited speed (in travel mode)
- Moderate increase in inertia (mod A), high increase of inertia (mod B)
- booster speed remains (inertia kicks in) unless you settle throttle again (for AI ships too)
- boosters last longer and are a true factor to differentiate agile ship (S/some M) from bulky ships
- boosters work as afterburners: while ships have low basic acceleration, the booster (rear engines) pushes the ship a lot.
- class specific equipments (combat items for combat ships only, etc.)
- race specific equipments (with many special items sold to all races and some crossovers)
- pirate ships can mount equipment from all races
- reduced/changed number of engines to 3 classes: basic, travel, combat
- added some special shields mk3
- rebalance of all hull/shields/weapons according to X3/X2 tradition (capital ships are strong!)
- changed shields to reflect the class: combat shields are fast to recharge, defence shields are slow to recharge but capable
- added a lot of turrets and guns and shields to several ships
- increased STORAGE for all trading/mining ships 2/3x
- rebalance of all prices/wares to reflect the value of big/capital ships and others
- Xenon/Khaak ships use different physics (vanilla kind), they are very agile and can accelerate faster. Xenon are machine btw, so acceleration is not an issue. Khaak are insects

- Xenon ships that the player can claim have peculiar physics that make them unique
- IMPORTANT: REM removes turrets from production modules (otherwise what are defence modules for?)
- Defence modules mount race-specific turrets/shields
NEW ship's role change/addition:
- changed all XL E carriers into battleships (much stronger but carry many less ships)
- changed Paranid Atlas Vanguard and Sentinel into: Atlas XL Trader and Atlas XL Miner (available also at Alliance, Hatikvah and Pirates)
- added some custom ships for specific tasks (that use vanilla models to avoid issues):
Phoenix E (as the E destroyer variant of paranid and Argon)