The Challenge Magazine PDFs are excellent digital reproductions of this classic RPG magazine. The page and cover scans range from good to excellent quality (the covers may show some signs of wear from the original), and all text is fully searchable. I just wish they had gone the extra step to bookmark them as well.
This particular issue has a wealth of information for the Twilight: 2000, MegaTraveller, Space: 1889 and Dark Conspiracy RPGs, plus articles for Shadowrun and Cyberpunk, and a Star Trek logic puzzle to solve. One page of this issue has been formatted upside down.