[immibis]

MMM++ is a variation of standard malloc/free. You can still UAF, but only to another object of the same type, which may or may not prevent an exploit.

Something that's missing is full-on formal verification where you write unrestricted C code and then mathematically prove it doesn't have any bugs. Nobody does this because proving a C program is correct is harder than mining a bitcoin block by hand, but it's useful to anchor one end of the safety/freedom spectrum. Many other approaches (such as borrow checking) can also be viewed as variants of this where you restrict the allowed program constructs to ones that are easier to prove things about.