FSet stands out here, among the collections libraries, as having the most features, the best-performing functional collections, the greatest convenience of use, and the most extensive documentation. cl-containers is also worth a look, if you want stateful collections. lisp-interface-library is interesting and has functional collections, but is nearly undocumented and is slower than FSet.

• access - Access is a library to ease getting and setting values in nested dictionary-like objects by providing a unified interface to hash-tables, clos-objects, plists and alists
• array-operations - Provides commonly used operations on arrays
• avl-tree - AVL (Adelson-Velsky-Landis) Tree is a self-balancing binary search tree implementation in Common Lisp
• B-Tries - A prototypical implementation of the data structure described in the paper "B-tries for disk-based string management" (PDF)
• binomial-heap - Binomial-heap is an implementation of the binomial heap data structure
• bk-tree - This page is moved to https://github.com/vy/bk-tree
• bknr-skip-list - An implementation of skip lists for bknr
• BST - BST is a Common Lisp library for working with binary search trees that can contain any kind of values
• cacle - cacle implements an extensible cache data structure
• cl-bloom - Bloom filters in Common Lisp with efficient hashing
• cl-btree - B-Tree implemented in Common Lisp
• cl-cache-tables - cl-cache-tables is a wrapper around native hash-tables to facilitate in-process caching of common lisp data structures
• cl-competitive - A code collection maintained mainly for competitive programming, and partly for just understanding algorithms
• cl-containers - cl-containers adds binary search trees, red-black trees, sparse arrays, and other useful containers
• cl-custom-hash-table - cl-custom-hash-table extends the hash table data structure by allowing the use of arbitrary TEST/HASH functions, in addition to the TEST functions allowed by the standard (EQ, EQL, EQUAL and EQUALP)
• cl-dawg - CL-DAWG is a DoubleArray/DAWG implementation
• cl-heap - CL-HEAP implements the binary heap, Fibonacci heap, and priority queue data structures
• cl-slice - This library was unmaintained for several years
• cl-speedy-queue - cl-speedy-queue is a portable, non-consing, optimized queue implementation
• cl-string-match - Provides substring (subsequence) search and text processing algorithms implementations including regular expression, prefix/suffix tree data structures, etc
• cl-treemaps - cl-treemaps is a lightweight and fast implementation of binary trees
• colliflower - Colliflower is a library for abstaractions around data structures
• D - The D Common Lisp library exists to enable using doubly-linked lists in a program using a style which resembles singly-linked lists as closely as reasonable
• data-table - data-table is a library providing a data structure that has rows of data and column names and types (ie database results)
• dawg - A DoubleArray / DAWG implementation
• dict - DICT is a hash table implementation
• dlist - dlist is a Common Lisp library that implements the doubly-linked list
• fare-utils - fare-utils is a collection of utilities from Fare Rideau
• fern - An efficient, consp, self-adjusting key-value trie-index abstraction for uuid namespaces
• Flexichain - Flexichain is an API for editable sequences
• folio2 - A collection of small libraries: functional idioms and data structures in Common Lisp and a common set of APIs for them
• FSet - FSet is a functional set-theoretic collections data structure library by _(Scott L
• Funds - Funds provides portable, purely functional data structures written in Common Lisp
• genhash - NET HEXAPODIA HASHTABLES is a data structure library for generic hash tables
• heap - Simple implementation of a binary heap for Common Lisp
• Heresy - Heresy is an implementation of the lazy list data structure
• hh-redblack - hh-redblack provides in-memory and disk-based red-black trees
• jarw-dictionary - jarw-dictionary is a generic map/dictionary interface with implementations using internal hash-tables, property lists, files and directories including in-memory caching
• jpl-queues - jpl-queues is a library implementing a few different kinds of queue data structures
• kdtree-jk - KDTREE-JK is a package for building efficent KD-Trees in Common Lisp
• lazy - This is a simple lazy form evaluation package for Common Lisp
• lisp-interface-library - lisp-interface-library is a collection of pure and stateful data structures in interface-passing style from Fare Rideau
• minheap - minheap provides several heap data structures with meldable min-heap and priority queue functionality
• multisets - Library of set operations on multisets
• nary-tree - The n-ary-tree package implements an automatically rebalancing B-tree data structure which supports n >= 5 items in any mixture of types per node
• NKeymaps - Emacs-style keymap management
• patty - Patty is a library that facilitates working with functional data structures on top of CLOS
• pileup - A portable, performant, and thread-safe binary heap / priority queue
• pipes - pipes implements the input stream (lazy list) data structure
• queues - A Common Lisp queue library with features such as non-consing thread safe queues and fibonacci priority queues
• quick-arrays - quick-arrays is a Debian package of the Quick Arrays concept
• Red-Black-trees - Red-Black-trees is an implementation of red-black-trees (a data structure)
• ropes - ropes is an implementation of the rope data structure, an alternative to strings with more efficient concatenation
• SEMI-PRECIOUS - SEMI-PRECIOUS is a library of algorithms/data structures
• Series - A library providing data structure that combines aspects of sequences, (lazy) streams and loops, using a technique known as “fusion” or “deforestation”
• spatial-trees - spatial-trees is a set of dynamic index data structures for spatially-extended data
• Sycamore - Sycamore implements several purely functional data structures in Common Lisp
• symbol-namespaces - symbol-namespaces defines a new kind of package that's named by a symbol rather than a string
• TREES - TREES provides several binary tree data structures exposed through a uniform CLOS interface
• versioned-objects - For any Common Lisp mutable object, allows to store versioning tree of all of the edits connecting its various versions
• vp-trees - vp-trees is an implementation of the vantage point tree data structure in Common Lisp
• X.FDATATYPES - XFDATATYPES implements 3 functional data structures:
• xsubseq - A version of subseq designed to minimize copying