Distributing and Managing Magento extension used to be a difficult and error prone process, that involved manually changing, uploading and updating files in more than one occasion that has resulted in unexpected promotions or deletions; sometimes permanent.
Recently Composer has been getting a lot of attention from the Magento community, and with good reason composer simplifies deployment and extension management.
Modman by Collin Mullenhour, Modman was a tool born out of necessity and is one of my preferred deployment tools both on development and production environments.
One of the more interesting features of modman is the ability to create symlinks to the particular Magento installation, I have found this feature to be particularly useful for testing extensions across multiple magento installations.
Instead of having multiple copies of the extension deployed across multiple development environments we can just reference a single common point through the symlinks. Any updates or changes that are made into this single point immediately take effect on all the symlinked installations.
Magento Connect is the name both used for the Magento extension market place and the package manager