Nunito Sans is free download available via an open source license. You’re free to use it.
Nunito Sans is a well balanced sans serif typeface superfamily. The project began with Nunito, created by Vernon Adams as a rounded terminal sans serif for display typography. Jacques Le Bailly extended it to a full set of weights, and an accompanying regular non-rounded terminal version, Nunito Sans.
These fonts are licensed under the Open Font License.
You can use them freely in your products & projects print or digital, commercial or otherwise.
This isn’t legal advice, please consider consulting a lawyer and see the full license for all details.