> Programs whose authors encourage the user to make donations are fine for the main distribution, provided that the authors do not claim that not donating is immoral, unethical, illegal or something similar; in such a case they must go in non-free.
BTW, the nagware code has been removed in Debian unstable:
1. It included a click-wrap agreement in violation of the Debian Free Software Guidelines.
2. Fishing for inappropriate citations should not be encouraged, as it compromises the integrity of scholarship.