Can I second this choice? My two maine coons love it - and even the semi-feral plays with it too. The 4 square 'hammocky' piece with buttons (not the hammock) is loved and disputed over.

It is configurable - you can add to make it bigger and to fit your space. it's like lego and it is sooooo easy to put together, unlike my other cat tree which was more expensive.

Edit: I forgot to say that it stands up to Maine coons playing ruff and tumble