As far as I can remember, Abaqus has always offered the possibility to extend or customize the functionality by means of user subroutines. Proprietary materials or elements arguably place the highest demands on the user, subroutines for controlling node temperatures or heat fluxes provide useful additions for applying loads. The list of possible user subroutines for Abaqus/Standard and Abaqus/Explicit is very long. User subroutines are written in FORTRAN, C or C++. The most common is probably FORTRAN.
In our WIKI article ‘Abaqus Unified FEA: Fortran Compiler‘ we present in detail how to select, install and run a FORTRAN compiler. At the moment, we are still limited to the Windows operating system from Microsoft. The requirements on a computer with Linux as operating system are rather lower, the installation and operation easier. As a manufacturer of a FORTRAN compiler only Intel remains at present. The use of open source compilers is not yet supported.
With oneAPI, Intel has combined many compilers and tools for software development. The topic has already been discussed in various places. Here, according to our current knowledge (May 2023), the use of a free version is basically feasible. With the restriction that only the latest release is available. However, this does not seem to be a fundamental obstacle.
The close connection to the Windows libraries means that, in addition to the FORTRAN compiler, a version of Microsoft Visual Studio is also required. There is still a free version of this, but only very few customers are likely to meet the requirements for this license.
Since user subroutines can be compiled on one computer and used on another, a minimal installation seems possible in principle.
But the costs are not, or should not be, in proportion to the benefits to be gained from the use of user subroutines. A benefit in the form of an extension of the application width, the improvement of the statement quality of a calculation or the shortening of calculation and processing times should be aimed at. We are happy to support you in selecting the right user subroutines and building your FORTRAN code.