You do realize Interchange and Agora are included with the Cpanel product free of charge? Interchange (interchange.redhat.com), is a much more advanced cart while Agora is quite straightforward and much easier if you are just starting out. Agora is extremely simple to tie in to CC processors, though it doesn't pack the feature-rich punch that interchange does.
Interchange is exceedingly difficult to manage/support from the sys admin/support standpoint however,
Just FYI