New features in <i>ATSAS-4</i> , a program suite for small-angle scattering data analysis

The <i>ATSAS</i> release 4 series introduces substantial architectural updates and enhanced user-friendly tools for analyzing biological macromolecules and nanostructured objects. In particular, highly requested project support for graphical user interfaces (GUIs) has been implemented. Here the state of the main window of each GUI application can be saved as a project and then restored to continue or extend analyses. All GUI applications now share a common framework, enabling various plot annotations and export as figures or text for easy data exchange with other plotting applications. The main interactive data processing and interpretation program, <i>PRIMUS</i>, has been significantly expanded with new features and integrated analysis modules. A new GUI for the program <i>PEAK</i> allows for multiple fitting functions, including Gaussian, Lorentzian and pseudo-Voigt. The online chromatography analysis program <i>CHROMIXS</i> supports multiple frame selections and subtractions, along with a newly included <i>EFAMIX</i> module for resolving partially overlapping components. The new <i>ATSAS</i> application <i>LAUNCHER</i> provides user-friendly wizards to configure and run command-line applications. Wherever feasible, operations like file reading and calculations have been parallelized to take advantage of available local compute resources. Command-line interfaces of many applications have been updated, <i>e.g.</i> with renaming and unification of common options. Improved readers/writers are implemented for Protein Data Bank and macromolecular CIF (mmCIF) file handling. The program <i>MIXTURES</i> now combines the functionalities of <i>BILMIX</i>, <i>LIPMIX</i> and <i>MIXTURE</i>, offering simplified and more versatile analyses for polydisperse systems of different shapes, also with single- or multi-layered organization. Installer packages of <i>ATSAS</i> are available for the latest versions of Windows, frequently used Linux distributions and recent macOS releases, both for Intel and ARM architectures, and are free for academic use.