Joomla! is a content management system (CMS) that focuses on creating and managing a wide range of content types, such as articles, blogs, and multimedia. It offers extensive customization options through its wide range of templates and extensions. On the other hand, OpenCart is an open-source e-commerce platform that specializes in creating online stores. It provides features specifically tailored for e-commerce websites, such as product listings, shopping carts, and payment gateways.

1. Target Audience: Joomla! is ideal for websites that require diverse content and extensive customization, making it suitable for businesses, blogs, and news websites. In contrast, OpenCart is designed specifically for online stores, providing specialized features for managing products, orders, and customer transactions.

2. Ease of Use: Joomla! is known for its user-friendly interface that allows users to easily create and manage content without much technical knowledge. OpenCart, however, may require a steeper learning curve as it focuses on e-commerce functionalities that may be more complex for novice users.

3. Community Support: Joomla! has a large and active community of developers and users who regularly contribute extensions, templates, and support resources. While OpenCart also has a supportive community, it may not be as extensive or diverse as Joomla!'s community.

4. Customization Capabilities: Joomla! offers a high level of customization with its wide range of templates and extensions that cater to various needs and industries. OpenCart also provides customization options, but they are more focused on e-commerce functionalities, such as product listings and checkout processes.

5. SEO Features: Joomla! includes built-in SEO features that help optimize websites for search engines, such as metadata management and URL customization. OpenCart also offers SEO tools, but they are more tailored towards enhancing product visibility and sales within an e-commerce context.

6. Scalability: Joomla! can handle larger and more complex websites with intricate content structures, making it suitable for growing businesses with diverse needs. OpenCart, while capable of handling medium-sized online stores, may face limitations in scalability when managing extensive product catalogs or high traffic volumes.

In Summary, Joomla! and OpenCart differ in their target audience, ease of use, community support, customization capabilities, SEO features, and scalability, catering to different needs in content management and e-commerce respectively.