Welcoming Repositories Index Fortran Ecosystem
Top Welcoming Open-Source Fortran Repositories
Top welcoming Fortran repositories. Scored by real 90-day external PR merge rates, maintainer review turnaround speed, and first-time contributor success.
Updated daily • Sat, 10 Oct 2026 UTC
Tracked Repos
106
>100 stars verified
Avg Merge Rate
67%
90-day external PRs
Open GFIs
61
Beginner friendly issues
Welcoming Tier
21
S & A Tier maintainers
Ranked Fortran Repositories
Showing top 50 of 106 ranked repositories
| Rank | Repository | Tier | Score | Merge Rate | Good First Issues |
|---|---|---|---|---|---|
| #1 | Wannier90: Maximally-localised Wannier functions for electronic-structure calculations (standalone code and Fortran/C/Python library) | S•Elite | 72.2 | 74.4% | - |
| #2 | Fire Dynamics Simulator | S•Elite | 70.8 | 87.3% | - |
| #3 | Exascale multiphase flow solver — 2025 Gordon Bell Prize Finalist | 200T grid points on 43K+ GPUs | A•Welcoming | 66.1 | 59.7% | 44 |
| #4 | cp2k/cp2k1,217 Quantum chemistry and solid state physics software package | A•Welcoming | 65.5 | 11.3% | 8 |
| #5 | cp2k/dbcsr156 DBCSR: Distributed Block Compressed Sparse Row matrix library | A•Welcoming | 64.4 | 91.7% | - |
| #6 | ESCOMP/CTSM352 Community Terrestrial Systems Model (includes the Community Land Model of CESM) | A•Welcoming | 64.2 | 35.0% | 4 |
| #7 | OpenRadioss is a powerful, industry-proven finite element solver for dynamic event analysis | A•Welcoming | 64.2 | 77.5% | - |
| #8 | dftd4/dftd4231 Generally Applicable Atomic-Charge Dependent London Dispersion Correction | A•Welcoming | 63.9 | 100.0% | - |
| #9 | Energy Exascale Earth System Model source code. NOTE: use "maint" branches for your work. Head of master is not validated. | A•Welcoming | 62.7 | 41.6% | 2 |
| #10 | USGS Modular Hydrologic Model | A•Welcoming | 62.5 | 59.5% | - |
| #11 | nasa/cea210 CEA computes the equilibrium composition of mixtures via free-energy minimization, and uses the resulting product concentrations to determine thermodynamic and transport properties. It includes a large database of species with thermodynamic curve-fit data, and can be used for rocket performance, detonation parameters, and shock-wave analysis. | A•Welcoming | 62.0 | 69.6% | - |
| #12 | NCAR/DART266 Data Assimilation Research Testbed | A•Welcoming | 61.5 | 83.3% | - |
| #13 | A library of modern Fortran modules for nonlinear optimization | B•Solid | 61.2 | 66.7% | - |
| #14 | LAPACK development repository | A•Welcoming | 61.0 | 54.5% | - |
| #15 | ElmerCSC/elmerfem1,729 Official git repository of Elmer FEM software | A•Welcoming | 60.8 | 65.2% | - |
| #16 | NOAA-EMC/WW3351 WAVEWATCH III | B•Solid | 60.8 | 80.0% | - |
| #17 | /ᐠ. ｡.ᐟ\ᵐᵉᵒʷˎˊ˗ | A•Welcoming | 59.7 | 38.5% | 1 |
| #18 | Main repository for the NLR-supported OpenFAST whole-turbine and FAST.Farm wind farm simulation codes. | A•Welcoming | 59.5 | 70.8% | - |
| #19 | Collection of builder repositories for BinaryBuilder.jl | A•Welcoming | 58.5 | 7.7% | - |
| #20 | CliMT/climt181 The official home of climt, a Python based climate modelling toolkit. | B•Solid | 58.3 | 83.3% | - |
| #21 | WRF-Hydro model code | B•Solid | 58.2 | 100.0% | - |
| #22 | M.I.T General Circulation Model master code and documentation repository | A•Welcoming | 57.9 | 60.0% | - |
| #23 | ROCm/aomp247 AOMP is an open source Clang/LLVM based compiler with added support for the OpenMP® API on Radeon™ GPUs. Use this repository for releases, issues, documentation, packaging, and examples. | A•Welcoming | 56.4 | 26.7% | - |
| #24 | Parallel Fortran Unit Testing Framework | B•Solid | 56.0 | 57.1% | - |
| #25 | MESAHub/mesa253 Modules for Experiments in Stellar Astrophysics | A•Welcoming | 56.0 | 38.1% | - |
| #26 | Fluidity | A•Welcoming | 55.7 | 66.7% | - |
| #27 | Collection of Fortran77 subroutines designed to solve large scale eigenvalue problems. | B•Solid | 55.4 | 100.0% | - |
| #28 | GFDL's Flexible Modeling System | B•Solid | 54.7 | 57.1% | - |
| #29 | The Earth System Modeling Framework (ESMF) is a suite of software tools for developing high-performance, multi-component Earth science modeling applications. | B•Solid | 54.7 | 80.0% | - |
| #30 | A code for fast, massively-parallel direct numerical simulations (DNS) of canonical flows | B•Solid | 52.8 | 100.0% | - |
| #31 | A library for directly calling PyTorch ML models from Fortran. | B•Solid | 52.4 | 12.5% | 2 |
| #32 | CP UMAT and CZM UEL for Abaqus | B•Solid | 51.8 | 100.0% | - |
| #33 | UFS Weather Model | B•Solid | 51.7 | 23.3% | - |
| #34 | GEOS-Chem "Science Codebase" repository. Contains GEOS-Chem science routines, run directory generation scripts, and interface code. This repository is used as a submodule within the GCClassic and GCHP wrappers, as well as in other modeling contexts (external ESMs). | B•Solid | 51.7 | 14.3% | - |
| #35 | myroms/roms142 Regional Ocean Modeling System (ROMS) | B•Solid | 51.4 | 100.0% | - |
| #36 | ECMWF OpenIFS model | B•Solid | 51.4 | 100.0% | - |
| #37 | Semiempirical Extended Tight-Binding Program Package | B•Solid | 50.7 | 100.0% | - |
| #38 | Official GitHub repository for netCDF-Fortran libraries, which depend on the netCDF C library. Install the netCDF C library first. | B•Solid | 50.0 | 100.0% | - |
| #39 | This is the GitHub repository for STELLOPT, the state-of-the-art stellarator optimization code. | B•Solid | 48.8 | 83.3% | - |
| #40 | NWChem: Open Source High-Performance Computational Chemistry | B•Solid | 48.7 | 75.0% | - |
| #41 | cmbant/CAMB260 Code for Anisotropies in the Microwave Background | B•Solid | 48.3 | 100.0% | - |
| #42 | Particle-in-cell code for plasma physics simulations | B•Solid | 48.2 | 100.0% | - |
| #43 | MPM3D-F90: An open source code for three dimensional material point method. | B•Solid | 48.0 | 100.0% | - |
| #44 | Repository for MPAS models and shared framework releases. | B•Solid | 48.0 | 50.0% | - |
| #45 | DFTB+ general package for performing fast atomistic simulations | B•Solid | 47.9 | 52.9% | - |
| #46 | HORSES3D: A high-order discontinuous Galerkin solver for flow simulations and multi-physics applications | B•Solid | 47.7 | 100.0% | - |
| #47 | The Temperature Dependent Effective Potentials (TDEP) code | B•Solid | 47.0 | 50.0% | - |
| #48 | Lightweight HDF5 polymorphic Fortran: h5write() h5read() | B•Solid | 45.9 | 100.0% | - |
| #49 | m3g/packmol381 Packmol - Initial configurations for molecular dynamics simulations | B•Solid | 45.2 | 0.0% | - |
| #50 | fortran-lang/fpm1,076 Fortran Package Manager (fpm) | B•Solid | 44.9 | 25.0% | - |
How to Get Your Fortran PR Merged
1
Check C-Rank™ First: Pick projects with S or A tiers to avoid maintainer ghosts and slow review cycles.
2
Run Local Verification: Ensure test suites and formatting linters pass before opening a pull request.
3
Submit in Maintainer Windows: Check the repository report card to submit when maintainers are most active.
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Frequently Asked Questions: Fortran Open Source
What is the most welcoming Fortran open-source repository?
The highest-ranked Fortran repository on GetMerged is currently wannier-developers/wannier90, with a C-Rank score of 72.2/100 and a 74.4% PR merge rate.
How can I find good first issues in Fortran?
You can browse verified beginner-friendly issues in Fortran by visiting our curated Good First Issues directory at getmerged.abhishekco.de/good-first-issue/fortran.
What makes a Fortran repository ‘Super Welcoming’ on GetMerged?
A ‘Super Welcoming’ (S-Tier) Fortran repository demonstrates an external PR merge rate above 80%, a median first response time within 24 to 48 hours, active review feedback, and clear onboarding documentation.