FileExt от Libor Benes

Features:
• Instant search: type an extension (e.g., .pdf, .docx) or any keyword.
• Comprehensive: extensions across all domains (documents, images, source code, archives, executables, and more).
• Reliable reference: includes both common and rare extensions.
• Professional use: designed for developers, sysadmins, educators, and power users.
• Offline and fast: no internet queries, everything is in the packaged database.

Security and Privacy:
• No permissions beyond clipboard (optional).
• No data collection or telemetry.
• No risky features, no external code.
• Flat file structure, pure HTML/CSS/JS.