One of the best free acoustic guitar plugins available. It offers a stunningly realistic sound and a built-in tab player. Spitfire Audio LABS (Free):

Includes realistic legato, glissando, natural vibrato, and even side noises like finger scratching to add "human" imperfections to a performance.

While these enhance realism, they don’t include mechanical “crackle.” To reach a “crackly… better” state, we layer post-processing within Kontakt and your DAW.

If the price tag is the barrier, you don't need a crack to get a great sound. Here are "better" ways to get that nylon vibe: Ample Guitar M Lite (Free):