Commercial applications are distributed on The AppExchange. You can also move code from one org to another using unmanaged packages, the metadata API and change set functionality.
- Publish Your First App with AppExchange Checkout - A detailed step by step guide on publishing your first app on the AppExchange.
- ISVForce Guide - A Must Read! This guide is written for independent software vendors (ISVs) who want to sell applications built on the Force.com platform. It covers the entire lifecycle of a packaged application.
- An Introduction to Packaging - This article provides an introduction to packaging and distribution on the Force.com platform
- Development Lifecycle Guide: Enterprise Development on the Force.com Platform [PDF]
- How IT can plan, build, test, and deploy Force.com applications using a combination of Web-based and traditional development practices.
- ISVforce Guide a.k.a. Developing Packages for Distribution [PDF]
- Everything you need to know if you're a developer building an app that will eventually be packaged on AppExchange.
- AppExchange Publishing Guide [PDF]
- How to publish an app or service on AppExchange so that it's available to external customers.
- Application Installation Guide [PDF]
- How to download apps into a Salesforce.com organization.