If you are looking for academic articles about stealth (low-observable) technology, several comprehensive reviews are available for free download in PDF format:
: An article exploring how modern radar systems (passive, multistatic, and IR) are being developed to counter stealth aircraft. Can be downloaded from ResearchGate . Stealth in Software & Marketing Stealth Free Download
: Occasionally, high-profile games are "stealth released" (launched without prior announcement) for free. For example, Konami recently released a free-to-play baseball title on the PlayStation Store. If you are looking for academic articles about
: A popular free stealth roguelike game created by Terry Cavanagh (of VVVVVV fame). It is a turn-based game where you must evade guards and cameras to reach an exit. You can play it online or download it for PC and OSX via the Tiny Heist official page. You can play it online or download it
: A detailed look at Radar Absorbent Materials (RAM) and methods for avoiding detection in aircraft. Available as a free PDF on Academia.edu .
: A review of how materials like graphene and carbon nanotubes are used to hide military vehicles from radar, available on ResearchGate .