I have developed quite a few e-commerce websites for software companies, and requirements are slightly different from standard e-commerce checkout process, as you can download the product at the end, and also need to cover specific requirements such as: how long is the download link available for, what to do if the download fails, etc.. etc..
There is now an e-commerce platform specially designed for software downloads: http://www.shareit.com
Big players such as AnyChart are using it, and I think it is worth considering for an e-commerce website selling software.