CMU Common Lisp VS femtolisp

CMUCL is a high-performance, free Common Lisp implementation.

Robust but lightweight and fast, scheme-like lisp implementation; only 150kb.

High-Performance Compiler
CMU Common Lisp features an efficient native code compiler that can produce highly optimized code for the supported platforms, enhancing performance for computationally-intensive applications.
Extensive Library Support
Includes a wide variety of libraries, providing functionality ranging from numerical computing to system interfacing, which allows developers to implement diverse applications without relying heavily on external packages.
Strong Typing System
CMUCL provides a strong type system with good error detection and optimization capabilities that can help catch errors at compile-time and improve runtime performance.
Garbage Collection
It includes an efficient garbage collector that manages memory naturally, minimizing manual intervention and reducing memory leaks and fragmentation in applications.
Comprehensive Integrated Development Environment
CMUCL comes with an integrated environment which includes a debugger, inspector, and an interface for efficient development and troubleshooting.

Limited Platform Support
The number of platforms explicitly supported by CMUCL is limited, which can be a constraint for developers who need to work across multiple or newer systems.
Steep Learning Curve
Newcomers might find CMUCL challenging due to its complexity and the intricate features specific to Lisp, requiring a steep learning curve compared to more modern languages and environments.
Outdated Documentation
Some users find the documentation to be outdated or not comprehensive enough, making it difficult to get started and fully leverage the system's capabilities.
Limited Community Support
The user and contributor community for CMUCL is relatively small compared to other languages and projects, which may result in less frequent updates and fewer third-party resources.
Complex Setup Process
Initial setup and configuration of CMUCL can be cumbersome, especially for users not familiar with Lisp environments or those who require specific custom configurations.