"If you are using this product for commercial use, you must make a one-time donation of $5 to the developer".
How about that?
Or we can have two $5 licenses:
- $5 Ware Life Time License
- $5 Ware Annual License
The $5 Ware Life Time License means a one-time donation. The $5 Ware Annual Licence means a $5 donation each year. $5 is not going to ruin anyone! Not even if paid once a year! Unless you are using hundreds or thousands of free programs.
But $5 will definately make some difference in income to the developer (compared to $0), and thus perhaps motivate the her / him to move the project forward a little faster. Who wants to do a $5 Ware License for the community?? :-)