In spite of the considerable effort put in developing Deriscope, I have decided to make it free for two reasons:
First because a large user group consists of individuals, such as students, who do not draw any immediate monetary benefit by using Deriscope. These people may find Deriscope helpful in furthering their future career prospects or expanding their intellectual horizons, but they often lack the financial means to pay for this extra help.
Second because of the fact that Deriscope is not a mature product and is therefore inevitably hampered by several types of deficiencies. My hope is to receive enough user feedback that will help me develop Deriscope to the next stage of perfection. In other words, your anticipated feedback carries for me a value that generally justifies the waving of the product's price.
However, in case you believe Deriscope has actually had a significant positive impact on your work, you may consider to reciprocate through a commensurate contribution so that I can continue to maintain and update this product.