Here you will find software that needs a little TLC to be "brought up to code". 

The "All-in-One" solutions are very attractive and promise to simplify much of what you do.  However, these are 'old' scripts that were great when they were new, but may not work as expected now.  This is because other services such as Authorize.net, PayPal, UPS, USPS, and others have changed the APIs used to connect to them over the years.  What this means to you is that you may need to hire a programmer to update the scripts to work as you need them.  Elance.com and RentaCoder.com are great places to post bid requests for this sort of thing.

The benefit to having these scripts, and the reason you may still want to consider them, is that they are sold as PLR (Private Label Rights) products that you may alter and resell as a new product of your own.  This means you don't have to start from square one to build a new product, and can take advantage of the huge development investments that were made to create these scripts in the first place.  This is particularly good if you are a programmer yourself and would like to gain a head-start on a much-needed product.  (If you produce such a script, I'd love to help you market it.)

The other benefit is that if you have relatively limited needs, they may serve you well with just a little fine tuning of the program code.

At the moment, there is only 1 script on the 'net that seems to be relatively current, and that's 1MerchantCart. 

Another alternative is JV Manager, which serves much the same purpose, but without built-in autoresponders.  The advantage to using this approach is that you can leave the headaches of insuring email delivery to another service, such as Aweber or GetResponse.