Use of Unity

can the free one be used commercially?

Yes, but only if you earn less the 100k a year.

Please note: Use of Unity Personal is
subject to certain limitations.

If your company currently makes more
than $100k in annual gross revenues or
has raised funds in excess of $100k,
you are not permitted to use Unity
Personal, for prototyping or
otherwise, as defined in our EULA
Agreement. You may use Unity Plus for
up to $200k in annual gross revenues,
or Unity Pro with an unlimited revenue
or fundraising capacity.
Download Unity Personal: Get Unity for Free | Unity