Possible:

• BuildCraft (local JSON index + Markdown entries)
• CoFH mods (remote Markdown index + Markdown entries; no search API, YAML-based navigation data)
• Immersive Engineering (langfile-based; partial - the guidebook's layout might be stored in code which is under a license we don't want)

Impossible:

• Tinker's book (from Mantle)?
• RTFM?