Low-level macros: MinimalSyntaxCaseCowan, explicit renaming, syntactic closures, R6RS syntax-case, SRFI 72.
Matching: MatchingWise
Combinators: CombinatorsCowan
Conditional procedures: ConditionalProceduresSamizdat
cond guards: SRFI 61
Lambda*:
Void: VoidCowan
Named parameters: NamedParametersCowan or SRFI 89
and-let*: SRFI 2
Generalized set!: SRFI 17, possibly plus Srfi17ExtensionsCowan
receive: SRFI 8
rec: SRFI 31
Cut/cute: SRFI 26
Loops: SRFI 42 or Riastradh's foof-loop or Chibi loop
Generic accessors/mutators: SRFI 123
Conditions: ConditionsCowan