Xmind in general is not solely a Windows-Tool. It is available on several other platforms. I list it here, because it nicely integrates with the PortableApps-stack.

Xmind is a good solution for Mind-Mapping. The free version usually suffices for me. Anyway, your mileage may vary. If you are more into project-management, the pro-features might be interesting to you.

Addendum: having reviewed the Xmind website, recently, I must say they clear turned towards commerce. Prices raised drastically. They do not advertise anymore, that they still have a free (i.e. non-Pro) version. I do not have the subscription, it appears simply too expensive for my taste, so I cannot even judge its real value, properly. I will look for more low-priced alternatives. For a manager who really uses all the project planning features, this should clearly be a good thing, but I only want to do mindmapping.