Back in 2012, Nik Software was purchased by Google. Pre-Google, the complete Nik Collection cost nearly $500. Then in 2013, Google slashed the price to around $150. Now it's on the house.
So why free? In this case it may be a good news/bad news scenario. Hard to beat free, but some also believe that this latest giveaway by Google may signal Nik's relegation to the land of "abandonware".
Even if that's the case, for the time being the Nik Collection is a high-end suite of software tools that you can take advantage of. You can download the Nik Collection here.