https://www.gamingonlinux.com/2016/03/cryengine-v-released-crytek-now-offer-cryengine-as-pay-what-you-want-source-code-access-too/
The last of the major engines has shaken up their business model into a pay what you want deal. They have also released CryEngine V with major new features.
cryengine vreleasedcrytekofferpay