Hrvatska is the native Croatian name for Croatia.
It's rather hard to pronounce in English as the letter "r" in the first syllable "hrv" is used more like a vowel (like in Trst), which doesn't happen in English. It's something like her-vah't-ska.
Croatia is the Latin version, but not all other languages use it, many use a form more similar to the native one. For example:
The country code for Croatia is HR (per ISO 3166), so Croatian Internet domains end with .hr.