Yes. Compound Interest Calculator is completely free, with no sign-up, no daily limit, and no watermark on what you download.
Compound interest is interest earned on both your original money and on the interest it has already earned. Over time this snowball effect makes your savings grow much faster than simple interest.
You can choose yearly, quarterly, monthly or daily compounding in the calculator. The more often interest compounds, the faster your money grows — daily compounding gives the highest return for the same rate.