Pelles C is freeware for any use: personal, commercial, etc. No registration is required to download it, and you can use it anonymously.
Pelles C can be freely distributed, but it can not be sold.
Pelles C is provided 'as-is', without any expressed or implied warranty. In no event will the author be held liable for any damages arising from the use of this software.
Pelles C is totally free. However, some users may want to express their gratitude by donating some money.
If Pelles C is a major part in building a product sold for money, it seems fair (to me) to donate a little bit of that money to Pelles C - but this is never required.
Donations will help to pay for this website, my time spent on support, and any possible new versions.