Literal lists are mutable: MIT, Gambit, Chicken, Guile, IronScheme, Bigloo, Loko, Chez, Mosh, Larceny, Vicare, Picrin, Schemik, TinyScheme
Literal lists are immutable: Cyclone, Chibi, Gauche, Sagittarius, Kawa, STklos, Scheme48
The following Schemes are known to use a special tag for pointers to pairs: MIT, T, Loko, Icarus/Vicare, Chez (definitely not Chibi, Chicken, pre-CS Racket)