As of 2016, is there a Scheme implementation which supports 100% of R7RS (small) with no deviations?
The Chairman of R7RS Small Language ("Working Group 1") committee, Alex Shinn, created Chibi Scheme as the standard evolved. I believe it is fully compliant. It is a bytecode compiler.
Larceny has a mostly (totally?) compliant R7RS mode, and compiles to machine code.
I have been playing with Picrin which aims for R7RS compliance, and is very very close. It is a bytecode compiler.
A list of implementations that are aiming for R7RS compliance at the committee's wiki include:
- Chibi
- Chicken (partial)
- Foment
- Gauche
- Guile (partial)
- Husk
- Kawa
- Larceny
- Mosh (partial)
- Picrin
- Sagittarius
Although the question explicitly excludes Racket from consideration as not being Scheme I will point to Racket package "R7RS" which implements R7Rs small.
There are some small incompatibilities documented on project's page.