Hi Stephanie,
Adobe Campaign Classic is a Windows-only local platform that delivers deep and rich campaign management and delivery options. It can be deployed on-premise, in a hybrid deployment or fully hosted option and for those marketers with more advanced data needs or who need a bit more customization, this is a very powerful solution for them.
See About Adobe Campaign Classic
Adobe Campaign Standard is a fully web-based, on-demand solution for cross-channel campaign management which also spans online and offline. ACS was built from the ground up to be available on any browser or device and largely leverages drag and drop for campaign management and content building. With many of the same capabilities of ACC, this is a great option for marketers who have more straightforward data management needs.
Hope this helps!
All the best,
Pablo