Reverbbot.com has everything to sell your software product online. All you need to do is to change content, upload your product's screenshot, videos etc and it will be ready. It has built in support for PayPal with IPN to collect payment. Most common features are: Login system, User panel (for customers to manage their account), Admin Panel (to modify anything you want), Captcha to stop spam, SEO ready, Auto cron jobs for database cleanup.
Link:Reverbnation BotTechnology Used:
ASP.NET, C# language, MSSQL Database, Visual Studio, MVC4, Razor, HTML5, CSS3