PMCs are Parrot's internal "classes". There are currently 5 abstract PMCs and 67 concrete PMCs.
Tools 
PMC-related tools.
classes/genclass.pl
Create a template PMC file.
classes/pmc2c.pl
PMC compiler (Old Version).
classes/pmc2c2.pl
PMC compiler (Version 2).
Abstract PMCs
These PMCs are not instantiated.
classes/default.pmc
Abstract root class.
classes/deleg_pmc.pmc
Delegate PMC.
classes/delegate.pmc
Delegate PMC.
classes/perlscalar.pmc
Perl Scalar.
classes/scalar.pmc
Scalar Abstract Superclass.
Concrete PMCs
These PMCs are instantiated.
classes/array.pmc
Array PMC.
classes/bigint.pmc
BigInt PMC class.
classes/boolean.pmc
Boolean PMC.
classes/closure.pmc
Closure PMC.
classes/compiler.pmc
Compiler PMC.
classes/complex.pmc
Complex Numbers PMC Class.
classes/continuation.pmc
Continuation PMC.
classes/coroutine.pmc
Co-Routine PMC.
classes/csub.pmc
C Subroutine PMC.
classes/enumerate.pmc
enumerate PMC.
classes/env.pmc
System Environment.
classes/eval.pmc
Dynamic code evaluation.
classes/exception.pmc
Exception PMC.
classes/exception_handler.pmc
Exception Handler PMC.
classes/fixedbooleanarray.pmc
fixed size array for booleans only.
classes/fixedfloatarray.pmc
fixed size array for floating point numbers only.
classes/fixedintegerarray.pmc
fixed size array for integers only.
classes/fixedpmcarray.pmc
fixed size array for PMCs only.
classes/fixedstringarray.pmc
fixed size array for strings only.
classes/float.pmc
Floating-point number.
classes/floatvalarray.pmc
Array of FLOATVALs.
classes/integer.pmc
Integer PMC class.
classes/intlist.pmc
Array of integers.
classes/iterator.pmc
Iterator PMC.
classes/key.pmc
Key PMC.
classes/multiarray.pmc
Multi-dimensional Array.
classes/nci.pmc
Naitive Call Interface.
classes/none.pmc
NULL.
classes/null.pmc
NULL.
classes/orderedhash.pmc
Ordered Hash.
classes/parrotclass.pmc
Parrot Class.
classes/parrotinterpreter.pmc
Parrot Interpreter.
classes/parrotio.pmc
Parrot IO.
classes/parrotlibrary.pmc
Dynamic Library.
classes/parrotobject.pmc
Parrot Object.
classes/parrotthread.pmc
Threaded Interpreter.
classes/perlarray.pmc
Perl Array.
classes/perlenv.pmc
Perl System Environment.
classes/perlhash.pmc
Perl Hash.
classes/perlint.pmc
Perl Integer.
classes/perlnum.pmc
Perl Floating-Point Number.
classes/perlstring.pmc
Perl String.
classes/perlundef.pmc
Perl Undef.
classes/pmcarray.pmc
PMC-only array class.
classes/pointer.pmc
Pointer.
classes/random.pmc
Random Numbers.
classes/ref.pmc
Reference to a PMC.
classes/resizablebooleanarray.pmc
resizable size array for booleans only.
classes/resizablefloatarray.pmc
resizable size array for floating point.
classes/resizableintegerarray.pmc
resizable size array for integers only.
classes/resizablepmcarray.pmc
resizable size array for PMCs only.
classes/resizablestringarray.pmc
resizable size array for strings only.
classes/retcontinuation.pmc
Return Continuation.
classes/sarray.pmc
Subroutine Parameter Array.
classes/scratchpad.pmc
Lexical Scrachpad.
classes/sharedref.pmc
Shared PMC Reference.
classes/slice.pmc
Slice PMC.
classes/string.pmc
String PMC Class.
classes/stringarray.pmc
String-only array class.
classes/sub.pmc
Subroutine.
classes/timer.pmc
Timer.
classes/tqueue.pmc
Threadsafe Queue.
classes/undef.pmc
Generic undefined value.
classes/unmanagedstruct.pmc
C struct with unmanaged memory.
classes/version.pmc
Version information.
classes/vtablecache.pmc
Hold a vtable pointer for later use.
