By definition, "massively multiplayer" games are always online, and most require some sort of continuous revenue (such as monthly subscriptions and advertisements) for maintenance and development purposes. Some games, such as Guild Wars, have disposed of the 'monthly fee' model entirely, and recover costs directly through sales of the software and associated expansion packs. Still others adopt a micropayment model where the core content is free, but players are given the option to purchase additional content, such as equipment, aesthetic items, or pets.