App markets are free in the sense that they are usually pre-loaded on mobile phones and other devices, but there is no such thing as a free app market or an app market that only offers applications which are free. There are several app markets, each offering tens of thousands of applications, free and paid ones alike. You may not be so lucky in finding a free app market, but there are more than enough free applications available from Android's Google Play, Apple's App Store, among others.
Dropbox, for example, is a free application from Google Play, which is not a free app market. This application allows the user to access as well as transfer files from any computer, as long as it also has Dropbox installed in it. Dropbox is also available to those who have either an iPad or an iPhone.
Another example of a free application that did not come from a free app market would be Triplt. It is from Apple's app store and works as an organizer on your iPhone for all of the travels that you plan to do, whether it be a business a trip or one for leisure. With this application, it will no longer be necessary to remember important details such as reservations.
Guidelines for mobile ads have been the focus of both the Mobile Marketing Association and the Interactive Advertising Bureau, but they are struggling to keep these guidelines up-to-date because of the frequent changes, brought about by its extremely speedy growth.