Racket, Gauche, Gambit, Chicken, Bigloo, scsh, Guile, Kawa, Chibi, Chez, Vicare, Larceny, Ypsilon, Mosh, IronScheme, NexJ, KSi, SigScheme, Shoe, RScheme, S7, BDC, Rep, Schemik, Llava, Sizzle, Spark, Femtolisp, Dfsch, Owl Lisp, Sagittarius return #f to (eq? 't 'T).
MIT, Scheme48, SISC, SCM, STklos, TinyScheme, Scheme 9, Dream, XLisp, Elk, UMB, VX, Oaklisp, SXM, Inlab return #t.
Preferred case is upper case
I also decided to check the case-insensitive implementations using (string=? (symbol->string 't) "T") to see which ones converted symbols to upper case internally. Only XLisp (which is not really Scheme-compliant) and Oaklisp (which is somewhat R3RS-compliant) did so.
Is #\Space a valid constant?
Racket, Gauche, MIT, Bigloo, Scheme48, Guile, Kawa, Chibi, Chez, NexJ, STklos, KSi, SigScheme, TinyScheme, Scheme 9, Dream, RScheme, Rep, Elk, Oaklisp, Llava, SXM, Spark, Dfsch, Inlab accept #\Space.
Gambit, Chicken, scsh, Vicare, Ypsilon, Mosh, IronScheme, Shoe, S7, Schemik, UMB, Sizzle, FemtoLisp, Owl Lisp, Sagittarius reject #\Space.
Gambit, TinyScheme, S7, VX, Sizzle, Owl Lisp do not accept #T as equivalent to #t.
The other Schemes in the test suite do.
All Schemes in the test suite accept E as well as e in inexact constants (except those without inexact number support).