From Homestar Runner Wiki
Fretmagic is a music magazine in Free Country, USA. Homestar tried selling Fretmagic, Teen Fretmagic, and Fretmagic Kids! to raise money for a free trip to Acapulco in the Strong Bad Email privileges, but the magazines ended up getting torched by The Cheat with the BMW Lighter.
The guitar on the cover is the Gibson Flying V. There is an article inside about Gary Palaroncini from Limozeen, and how he mastered the hardest chord ever on an Ibanez G800-XV. This chord is a combination of a diminished 9th and a demonished 10th and requires eleven fingers. According to the article, his mother is very proud.