Instead of Lean
Lean alternatives
Lean brings programming and proof work together: it is a functional language for general coding and a proof assistant for formalized mathematics and software verification. Its small trusted kernel checks proofs, Grind automates some pattern matching and case analysis, and Mathlib offers a large community mathematical library. Lake manages projects, and users can work through editor integrations or run Lean in a browser. It is free and open source, with Linux, macOS, Windows, and web options.
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Rocq
Free plan ExtensionLinuxMac+2Interactive proofs and certified program extraction — Rocq uses Gallina for mathematical specifications and proofs, and can extract certified programs to OCaml, Haskell, or Scheme.
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Z3
Free plan AndroidAPILinux+4SMT solving with broad language interfaces — Z3 focuses on satisfiability modulo theories, accepts SMTLIB2 by default, and documents interfaces for many programming languages.
Free plan Visit site - 3
Boogie
Free plan LinuxMacWindowsBuilding verifiers for other programming languages — Boogie is a modeling layer that generates verification conditions for an SMT solver, with Z3 as its default.
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cvc5
Free plan APILinuxMac+3Automatic SMT solving and function synthesis — cvc5 solves SMT problems and includes a SyGuS engine for synthesizing functions against background theories.
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HOL4
Free plan LinuxMacSelf-hosted+1Higher-order logic and interactive theorem proving — HOL4 centers on higher-order logic and combines deduction, execution, property checking, and tools for building proofs.
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PVS
Free plan LinuxMacWindowsFormal specification with an integrated proof environment — PVS bundles a specification language, predefined theories, an interactive prover, symbolic model checker, and GNU or X Emacs interface.
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Why3
Free plan APILinuxSelf-hosted+2Deductive program verification through external provers — Why3 uses WhyML to generate verification conditions for external provers and can extract WhyML programs into OCaml.
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Alloy Analyzer
Free plan APILinuxMac+1 - 9
CBMC
Free plan LinuxMacSelf-hosted+1 - 10
CPAchecker
Free plan LinuxMacSelf-hosted+1 - 11
F*
Free plan LinuxMacSelf-hosted+1 - 12
ACL2
Free plan LinuxMacSelf-hosted+1 - 13
Agda
Free plan ExtensionLinuxMac+3 - 14
Isabelle
Free plan LinuxMacSelf-hosted+1 - 15
OpenJML
Free plan APIExtensionLinux+2 - 16
Apalache
Free plan APILinuxSelf-hosted - 17
Dafny
Free plan LinuxMacSelf-hosted+1 - 18
NuSMV
Free plan LinuxMacWindows - 19
HOL Light
Free plan LinuxMacSelf-hosted+2 - 20
K Framework
Free plan APILinuxMac+1 - 21
PRISM
Free plan LinuxMacWindows - 22
Frama-C
Free plan LinuxMacWindows - 23
TLA+
Free plan ExtensionLinuxMac+1 - 24
VeriFast
Free plan ExtensionLinuxMac+1 - 25
SPIN
Free plan LinuxMacWindows
A different tool may suit you better if you need a narrower verification workflow, a particular input format, or a solver to connect to other tools. Rocq can extract certified programs; Z3 and cvc5 center on SMT solving; Boogie generates verification conditions for an SMT solver. HOL4 and PVS offer interactive proof environments, while Why3 routes program verification conditions to external provers. Compare how each represents your problem, the automation and integrations it provides, and any setup or licensing conditions. All six alternatives are free, but each focuses on a different kind of proof or verification work than Lean's combined language-and-assistant approach.