You can use, but for the money. If no — please provide the source code under the GPL, which is not very crossed with commercial products. Note, commercial product — not just the one for which you pay the money, roughly speaking, earn money and opensource, and there's a commercial secret. Although, of course, all depends on the individual case of default. I at the time when the boss didn't want to buy the ExtJS license, got out with YUI, it was also a huge commercial backend monster.