.odt files

I recently received a document from a friend via e-mail before she left for holidays...I can't open it....it has an .odt file....I've never heard of it....I looked it up briefly to see if i could convert it to a word document, but no such luck....anybody have any experience with this file type that could tell me how to open it??? It's a schedule. Thank you so much!

 

Thank you so much! I downloaded the program and all works smoothly so far!!! Very much appreciate your help!