You could do the equivalent of shareware---every once in a while, instead of processing a query or transformation, return a "freeLoader-type" exception... ;)

Seriously though, maybe a warning when the user tried a download, that without making a small donation (payment options available at a click) and/or without reaching a total donation amount, the product will need to become more expensive (and closed) for everyone... You could require registration for a download at your site and send reminders.. I think people need it a little in their face, a little reminding, perhaps a little guilt, and very easy options to pay and get it out of the way quickly.

Brett

Andrew Welch wrote:
I wrote:
  
... and the donation system doesn't really work.
    

Just to put that into perspective - Saxon had around 125,000 downloads
over the last year, so if 10% of downloaders dontated $10 each, you'd
get the $100k figure that's hoped to be raised by licensing Saxon-B.
If companies donated a more appropriate amount of $1000, then it would
take just 0.01%

I wonder if it would be possible to keep Saxon as a free product if
there was a concerted effort to get the donations flowing from large
companies and individuals with a vested interest - or if its too late?