Twinkle is a totally free open source product. You can download it at no charge. I have created Twinkle just for fun. However, if you like Twinkle so much and want to donate a few Euro's that you saved on your telecommunications bill , feel free to do so.
Note that donations do not grant you any service support or product improvements. The donations are only for the product as is. Twinkle comes with ABSOLUTELY NO WARRANTY.