The ATSAS program package (version 2.4) has been updated to enhance the processing and analysis of isotropic small-angle scattering (SAS) data. Key developments include multiplatform data manipulation and visualization tools, automated data processing, improved integration of high- and low-resolution models from other structural methods, new algorithms for building 3D models from weakly interacting systems, and enhanced tools for analyzing mixtures and flexible systems. The new release includes installers for Windows, Linux, and Mac OS X, and provides improved indexed documentation. Web-based services, including a user forum and online access to run ATSAS programs, are also described. The paper describes major recent developments in ATSAS, including improvements in existing programs and the addition of new programs. The main aim is to provide a concise description of the new ATSAS features. The paper also describes new and improved ATSAS-related services, including multiplatform installers, online help documentation, and a web user forum for discussing and resolving software issues. The first release of the graphical data analysis program PRIMUS was designed for the Microsoft Windows operating system. With the release of ATSAS 2.4, a cross-platform implementation of PRIMUS is provided, which also includes a cross-platform version of the data visualization utility SASPLOT. The applications are based on the Qt graphical user interface toolkit. Though the Qt PRIMUS implementation has fewer features than its Windows counterpart, basic data visualization in various scaling schemes is provided. Advanced zooming and panning of the canvas is available within the data manipulation screen of Qt PRIMUS. Basic operations for file manipulation and processing are present, including averaging, subtraction, adjustment, scaling, and merging of data sets. The new PRIMUS can load a virtually unlimited number of files, compared to the previous limitation of 12, and keeps a list of recently used files for quick access. A new program, AUTOMERGE, has been designed for automatic extrapolation and merging of several data sets collected on the same sample at different solute concentrations. AUTOMERGE scales a set of input scattering profiles to obtain a reliable profile overlap and checks that the sample identity is qualitatively consistent across the series. It further determines the intensity extrapolated to infinite dilution, assuming a linear relationship between the intensity and solute concentration. The validity of the extrapolation to zero concentration is controlled by diagnostic tools that compare expected output with the actual estimate. The primary quality check of the extrapolation is performed by comparison of the radius of gyration value for the extrapolated curve and the linear extrapolation of Rg values from all input profiles. Additionally, a check on the pointwise error of linear extrapolation is performed, using standard procedures for least-squares approximation. The molecular mass (MM) of the particle is one of the major overall parameters that can be directly deduced from the experimental solution scattering data. This parameter allows one to determine the oligomeric state of homThe ATSAS program package (version 2.4) has been updated to enhance the processing and analysis of isotropic small-angle scattering (SAS) data. Key developments include multiplatform data manipulation and visualization tools, automated data processing, improved integration of high- and low-resolution models from other structural methods, new algorithms for building 3D models from weakly interacting systems, and enhanced tools for analyzing mixtures and flexible systems. The new release includes installers for Windows, Linux, and Mac OS X, and provides improved indexed documentation. Web-based services, including a user forum and online access to run ATSAS programs, are also described. The paper describes major recent developments in ATSAS, including improvements in existing programs and the addition of new programs. The main aim is to provide a concise description of the new ATSAS features. The paper also describes new and improved ATSAS-related services, including multiplatform installers, online help documentation, and a web user forum for discussing and resolving software issues. The first release of the graphical data analysis program PRIMUS was designed for the Microsoft Windows operating system. With the release of ATSAS 2.4, a cross-platform implementation of PRIMUS is provided, which also includes a cross-platform version of the data visualization utility SASPLOT. The applications are based on the Qt graphical user interface toolkit. Though the Qt PRIMUS implementation has fewer features than its Windows counterpart, basic data visualization in various scaling schemes is provided. Advanced zooming and panning of the canvas is available within the data manipulation screen of Qt PRIMUS. Basic operations for file manipulation and processing are present, including averaging, subtraction, adjustment, scaling, and merging of data sets. The new PRIMUS can load a virtually unlimited number of files, compared to the previous limitation of 12, and keeps a list of recently used files for quick access. A new program, AUTOMERGE, has been designed for automatic extrapolation and merging of several data sets collected on the same sample at different solute concentrations. AUTOMERGE scales a set of input scattering profiles to obtain a reliable profile overlap and checks that the sample identity is qualitatively consistent across the series. It further determines the intensity extrapolated to infinite dilution, assuming a linear relationship between the intensity and solute concentration. The validity of the extrapolation to zero concentration is controlled by diagnostic tools that compare expected output with the actual estimate. The primary quality check of the extrapolation is performed by comparison of the radius of gyration value for the extrapolated curve and the linear extrapolation of Rg values from all input profiles. Additionally, a check on the pointwise error of linear extrapolation is performed, using standard procedures for least-squares approximation. The molecular mass (MM) of the particle is one of the major overall parameters that can be directly deduced from the experimental solution scattering data. This parameter allows one to determine the oligomeric state of hom