Allegro CL provides the full American National Standards Institute (ANSI) Common Lisp standard with many extensions, including threads, CLOS streams, CLOS MOP, Unicode, SSL streams, implementations of various Internet protocols, OpenGL interface.

[4] Allegro CL is available for many operating systems including Microsoft Windows (32/64-bit), and many Unix and Unix-like, 32-bit or 64-bit, including macOS (Intel, 32/64-bit), Linux (32/64-bit), FreeBSD (32-bit), Solaris (x64, SPARC; 32/64-bit), UNICOS, and UTS.

Allegro CL can be used with and without its integrated development environment (IDE), which is available for Windows, Linux, and on macOS in version 8.2.

Allegro CL is available as freeware, a Free Express Edition (with some limits like a constrained heap space) for non-commercial use.

Allegro CL includes an implementation of Prolog[6] and an object caching database called AllegroCache.