There are many software mind mapping packages available including the "official" mindmap program from Tony Buzan's organisation - imindmap.
Xmind is a freeware program (now at version 8) that is available on all platforms (windows, apple, android) and in our view is as good as any of the paid programs. There is a professional version of the program which does have a cost but the extra features in this version only make any sense for an organisation or a professional working for one.
We strongly recommend that you try this program. You can get it here.
One other advantage of Xmind is that it is one of the main formats used by the mindmap collection site Biggerplate which gives thousands of predone mindmaps for many subjects.
Biggerplate reviews and grades the different mindmap software out there. Currently Xmind comes 4th. But the first three cost significant amounts to purchase/lease (£65, £70 and £120 for top 3). Many companies use these paid versions but in my review of their trial versions Xmind is really almost as good as all of them and did I say it is free.