Thin wrapper over atomic operators such as Compare and Swap (CAS).
Basic multithreading constructs including locks and condition variables.
Direct memory manipulation and interaction with foreign libraries following the C ABIs.
Environment introspection as described in CLtL2.
Common Lisp Abstract Syntax Tree introspection (with CLtL2 environments).
For the common Meta-Object Protocol extension to CLOS.
Portable definitions reflection library, including source location tracking.
Capturing the call stack and inspecting frames.
IEEE floating point number extensions such as infinities, NaN handling, and trap masking.
Unrebindable global variables.
Compile-time introspection of environments.
Allow for exiting the Lisp process.
Simple arrays that don't move in memory and can be shared with foreign systems.
Retrieve the lambda-list of a function.
Printing the current stack trace to a string.
Some of the extensions described in CLtL2 that were not included in ANSI.
Allows arbitrary functions to become the standard Lisp debugger
Custom sequence classes through a CLOS protocol.
Standardised platform features for CPU architectures and operating systems.
Query a file's size from its metadata.
Access to GC related tasks such as weak pointers, weak tables, and finalizers.
Custom stream classes through a CLOS protocol.
Provide a portable macroexpand-all function.
Package nicknames that are local to another package, avoiding package naming conflicts.
Allows macro writers to provide better feedback to macro users when errors are signaled during macroexpansion.
The general toolkit library shipped with ASDF. Handles pathnames, filesystems, external processes, and more.
POSIX/BSD sockets to establish TCP or UPD connections and servers.