Chiming in to shill my recently launched fixed-point math library, PRBMath.
The nice thing about PRBMath is that it ticks off all requirements that have been discussed in Designing Fixed Point Math in OpenZeppelin Contracts. It operates with 256-bit word sizes, it has a fixed number of 18 decimals, and it supports both signed and unsigned numbers. But PRBMath doesn’t compromise on gas efficiency - it is comparable in gas prices to ABDKMath64x64, which is known to be efficient.