Amember works as a standalone script, however it integrates with your WordPress website. It can also integrate with other platforms such as forums, affiliate scripts, help desk software, email systems, and image galleries. The software also supports every payment processor you can think of and has a built-in affiliate program to help promote your website.
It supports unlimited membership levels and subscriptions and allows you to promote your website using discount codes. Content can be dripped to members and there is an option to protect files too.
Pricing: $179.95 ( six months of updates and support)