This priority queue is licensed under the MIT license. That means it's free to use in all cases: free for personal or commercial use, in free or paid software, open or closed source. No strings attached!
If you're going to use this in a commercial application, I'd appreciate it if you emailed me to let me know my efforts are being put to good use. You're also welcome to thank me in the credits :) However, neither of these things are strictly necessary.
And of course, no warranty is provided.