In AppExchange’s huge repository, some apps are free, while many carry a subscription fee. Apps are categorized in three main ways:

By type (apps, components, Lightning Bolt solutions)
By product (sales, services, marketing, etc.)
By industry (government, education, finance, etc.)
Salesforce AppExchange products come in two flavors: Managed packages and unmanaged packages.

Unmanaged packages are typically used to distribute open-source projects and applications so that developers have the basic building blocks of functionality. They can then later build additional functionality on top of it, or make a modification to the project based on their requirements, e.g., business logic. Once it’s distributed, an unmanaged package cannot be upgraded.

Managed packages are typically built by Salesforce ISV partners to sell and distribute their applications to customers. These packages are created from Salesforce Developer Edition organizations. Managed packages are fully upgradable. The customer installing the package cannot see or make changes to Apex code that is part of a managed package.