It may surpise you to learn that in much of Latin America, there is an alternate form for the familiar/friendly you.  It is the word vos. Although its use varies from region to region and its consideration as standard Spanish varies widely from country to country, you can hear vos used in regions in many countries of Central America as well as in the countries of the Southern Cone (Chile, Argentina, Uruguay) as well as in parts of Colombia, Peru, and Ecuador.

However, before this happened vos came to be used in a different way than in its original Latin and later Spanish use.  In Latin and in early Spanish vos was used to address a group of people.  For example if you asked a group of people in the early middle ages if they were travelling to Santiago de Compostela, you would ask, "¿Viajades a Santiago de Compostela?"

However, during the medieval period the meaning of vos expanded.  In order to show repect to a fellow noble, people from the upper classes of society began to use vos when they were only talking to one person.  Nevertheless, this was not a uniform standard as many documents written in this period often show a mixture of a use of tú and vos by one person during a single conversation.  It was precisely around this time that Spain was exploring the Americas.  So this flux between tú and vos was brought to the Americas with the Spaniards.

In Spain the tú/vos flux was resolved in the eventual elimination of vos with the polite address instead using vuestra merced which literally means "your mercy" and might compared to the use of Your Highness in English used to address royalty.
Vuestra merced, since it didn't mean "you", took the same verb form as él and ella, and for the same reason the plural  vuestras mercedes tooke the same form of the verb as ellos and ellas.  You may have guessed already that vuestra mercedand vuestras mercedes came to be shortened to the familiar usted and ustedes form.

In parts of America where there was a strong influence of the Spanish Court, places such as Mexico and Peru, the eventual change from vos to tú and vuestra merced /Ud. mirrored the evolution in Spain.  However in regions farther away from the centers of power this evolution did not necessarily follow the same pattern.  Instead, in some regions tú was displaced by vos  in the friendly address and Ud. was used in the polite address. Although some people attribute this displacement to the lack of education of the Spanish explorers in the regions where tú is now used.  Recent studies seem to indicate a much more complex evolution. For that reason vos can be found in many parts of America and the verb forms that accompany vos vary more than one might expect.