Fretello - Duolingo for learning how to play guitar
Zotero - Zotero is a free, easy-to-use tool to help you collect, organize, cite, and share research.
Justin Guitar - Over 750 completely free guitar lessons!
Qiqqa - Qiqqa is a free research and reference management software. It can be used in many organizational projects from the academic to the personal to the business endeavor. Read more about Qiqqa.
Uberchord Guitar - Get better on your guitar. Fast.
JabRef - Graphical Java application for managing bibtex (. bib) databases.JabRef · JabRef Help · JabRef | Blog · OpenOffice/LibreOffice .