thank you for the message. As you know our Family Tree Builder software doesn't have a Mac version yet.
We've received many requests for this, so producing a Mac version is definitely in our plans. In the meantime, you can wait until we have a Mac version, or continue to grow your tree online. We are very sorry, but we can not provide any time frame, when it can be launch.
By the way, did you try/or consider to install Windows version on Mac - it can maybe works for you in that way for Family Tree Builder.