The brazilian Viola Caipira has nothing to do with the orchestral Viola, used mostly in classical performances. It was brought to Brazil by the first portuguese people, and modified and evolved, making it almost a genuine, Brazilian-only instrument now.
It is used mostly on country-side small cities or farm regions of Brazil. And songs played with Viola Caipira sound like these places: home-made food, green landscapes, country life.
Almir Sater is a well known violeiro that used to be more active with the viola, and as an example, one of its beautiful compositions, Luzeiro, was used to open an old TV show focused on farming.
There are other excellent violeiros, as Paulo Freire [blog], Roberto Correa, Ivan Vilela, Braz da Viola and many others. Levi Ramiro is one of my favorites, with its Estiva Grande.
Songs played with Viola use to be accompanied by a Rabeca, a sort of simplified violin. Luis Eduardo Gramani was one of our masters in Rabeca compositions, writing beautiful songs as Deodora.
Do not forget to right click on each song link to download the hi-fi MP3 file.