ASWNS

ASWNS ("Arcetri-Stockholm-Warsaw Neutron Star", from the names of the cities where it has been developed) is a FORTRAN 90 code that solves for the structure of rotating neutron stars in the "eXtended Conformal Flatness Condition" (XCFC) approximation of general relativity.
It assumes stationarity, axisymmetry, and circularity (the matter motion is purely toroidal).
The neutron star can be in rigid or differential rotation, cold or hot, barotropic (i.e. the equation of state is effectively barotropic) or nonbarotropic (i.e. baroclinic).

ASWNS is a fork of the XNS-v2 code described in [1] and [2] and has been used in [3] to determine the mass that would escape black hole formation after the collapse of a cold neutron star in rigid rotation at the Keplerian limit, in [4] to break the assumption of effectively barotropic neutron star, and in [5] to model the hot, nonbarotropic, and differentially rotating binary neutron star merger remnant.
Contrary to XNS-v2, ASWNS employs the self-consistent-field method, it does not assume a barotropic equation of state and therefore the star can be nonbarotropic (see [4] and [5]), and it does not solve for magnetic configurations (see [2]).

Note that the published version of the code ASWNS is not exactly the same used in [3, 4, 5], but it is very similar to the latter (i.e. [5]), even if the examples of usage of ASWNS are based on [3] and [4].
I decided not to provide the implementation of the model of the merger remnant of [5] not to obscure with technical complications the structure of the code.
You can implement any neutron star model on top of ASWNS, as shown in the examples provided.

If you use ASWNS, please cite:

* [1] Bucciantini & Del Zanna (2011), "General relativistic magnetohydrodynamics in axisymmetric dynamical spacetimes: the X-ECHO code", A&A 528:A101, arXiv:1010.3532
* [2] Pili, Bucciantini & Del Zanna (2014), "Axisymmetric equilibrium models for magnetized neutron stars in General Relativity under the Conformally Flat Condition", MNRAS 439:3541, arXiv:1401.4308
* [3] Camelio, Dietrich & Rosswog (2018), "Disc formation in the collapse of supramassive neutron stars", MNRAS 480:5272, arXiv:1806.07775
* [4] Camelio, Dietrich, Marques & Rosswog (2019), "Rotating neutron stars with nonbarotropic thermal profile", PRD 100:123001, arXiv:1908.11258
* [5] Camelio, Dietrich, Rosswog & Haskell (2021), "Axisymmetric models for neutron star merger remnants with realistic thermal and rotational profiles", PRD 103:063014, arXiv:2011.10557