Hi Balázs,
Thanks for reaching out!
We do have a Nonprofit Partnership Program, which offers free versions of Events Calendar Pro and Event Tickets Plus to approved organizations (although please note that our free licenses do not include premium support as our paid licenses do). In order to apply, you do need to be a 501(c)3 or 501(c)19 organization, so unfortunately this only applies to organizations within the United States. If you are a US organization, then please submit an application here, and we will get back to you as soon as we can!
However, our other extensions are not currently part of that program. We do occasionally run promotions, so I would definitely recommend subscribing to our newsletter so that you can stay up to date!
If you have any questions, please let me know.
Thanks,
Jennifer