If one were to name the single most important C++ library or library suite, it would undoubtedly be the Boost library suite. Boost provides free peer-reviewed portable C++ source libraries and “emphasize libraries that work well with the C++ Standard Library. Boost libraries are intended to be widely useful, and usable across a broad spectrum of applications. The Boost license encourages the use of Boost libraries for all users with minimal restrictions.”

The current release of Boost is 1.83.0. The next beta release is 1.84.0 beta 1. Here is the list of libraries currently included in Boost:

• Accumulators
• Algorithm
• Align
• Any
• Array
• Asio
• Assert
• Assign
• Atomic
• Beast
• Bimap
• Bind
• Call Traits
• CallableTraits
• Chrono
• Circular Buffer
• Compat
• Compatibility
• Compressed Pair
• Compute
• Concept Check
• Config
• Container
• Container Hash
• Context
• Contract
• Conversion
• Convert
• Core
• Coroutine (deprecated)
• Coroutine2
• CRC
• Date Time
• Describe
• DLL
• Dynamic Bitset
• Enable If
• Endian
• Exception
• Fiber
• Filesystem
• Flyweight
• Foreach
• Function
• Function Types
• Functional/Factory
• Functional/Forward
• Fusion
• Geometry
• GIL
• Graph
• GraphParallel
• Hana
• Heap
• Histogram
• HOF
• ICL
• Integer
• Interprocess
• Interval
• Intrusive
• IO
• Iostreams
• Iterator
• JSON
• Lambda
• Lambda2
• LEAF
• Lexical Cast
• Local Function
• Locale
• Lockfree
• Log
• Math
• Math Common Factor
• Math Octonion
• Math Quaternion
• Math/Special Functions
• Math/Statistical Distributions
• Member Function
• Meta State Machine
• Metaparse
• Min-Max
• Move
• Mp11
• MPI
• MPL
• Multi-Array
• Multi-Index
• Multiprecision
• MySQL
• Nowide
• Numeric Conversion
• Odeint
• Operators
• Optional
• Outcome
• Parameter
• Parameter Python Bindings
• PFR
• Phoenix
• Pointer Container
• PolyCollection
• Polygon
• Pool
• Predef
• Preprocessor
• Process
• Program Options
• Property Map
• Property Map (Parallel)
• Property Tree
• Proto
• Python
• QVM
• Random
• Range
• Ratio
• Rational
• Ref
• Regex
• Result Of
• Safe Numerics
• Scope Exit
• Serialization
• Signals2
• Smart Ptr
• Sort
• Spirit
• Spirit Classic
• Spirit Repository
• Stacktrace
• Statechart
• Static Assert
• Static String
• Stl_interfaces
• String Algo
• String Ref
• Swap
• System
• Test
• Thread
• ThrowException
• Timer
• Tokenizer
• Tribool
• TTI
• Tuple
• Type Erasure
• Type Index
• Type Traits
• Typeof
• uBLAS
• Units
• Unordered
• URL
• Utility
• Uuid
• Value Initialized
• Variant
• Variant2
• VMD
• Wave
• Xpressive
• YAP

Yes, it’s a very large library suite. You can find it here: https://www.boost.org/