Even if you don't plan to buy it, getting the demo installed is invaluable for testing before purchase.
Unlike standard samplers, Cuba uses a Rhythm Pattern engine. You don’t have to program MIDI notes for a conga pattern. You simply press middle C, and the instrument plays a Son montuno pattern. Press D, it changes to a Salsa pattern. This is revolutionary for songwriters who aren't percussionists. Even if you don't plan to buy it,
Short answer: No. Native Instruments does not offer a 100% free, standalone, permanent version of the Cuba library. You simply press middle C, and the instrument
Long answer: You can play the entire instrument for free, legally, for 15 minutes at a time. Furthermore, you can download a free "session" of pre-made sounds using the KOMPLETE START bundle. Short answer: No
If you see websites offering a "Cuba Kontakt .ISO" or "Cracked RAR file," ignore them. Piracy is rampant with NI products, but cracked versions are usually missing samples, contain malware, or crash your DAW. More importantly, they deprive the Cuban session musicians who recorded these samples of their royalties.
When you play a piano chord in Cuba, you aren't just hearing a piano. You are hearing a "Montuno" style piano recorded by a Cuban player. The swing feel is mathematically imperfect—it breathes. That is something generic sample packs cannot replicate.