You can create a download portal of third party software/application using WP Download Manager + WordPress PAD Importer add-on. PAD Importer creates new packages/downloads from a provided PAD file URL.
PAD® stands for the Portable Application Description specification and XML format. Software/Application authors and publishers provide product descriptions, requirements and other product-specific details to online sources, websites, and catalogs using PAD file. There is an official PAD repository where publishers list their PAD files.
The PAD standard saves time for publishers in distributing their products and for webmasters in updating, maintaining, and publishing products on their sites. If you want to build a download portal like Softpedia, Softonic you have to provide a way to create downloads from PAD files, as it is the widely recognized form of software distribution.