freeware vs libre software

freeware

noun
  • Complete and functional software that does not require payment or other compensation (such as viewing advertising) for its use. Freeware may be a proprietary license with no access to the source code. 

libre software

noun
  • Synonym of free software 

How often have the words freeware and libre software occurred in a corpus of books? (source: Google Ngram Viewer )