Want to use any open source stack for rapid erp development for a school. Which can be used for multiple site with multiple deployment. My preferred development stack is java/python/javascript. For that, I choose ERPNext. Is there any hidden cost or subscription required for the use of ERPNext? Can you please suggest me any alternative? Thanking you in advance.
It's free to use. No hidden costs. No subscription if you host it yourself, or you can pay them to host it for you.
But that does not mean it is not licenced.It is currently licenced under the GNU General Public License v3.0, so as long as you comply you are free to use it.
https://erpnext.com/docs/user/manual/en/introduction
https://erpnext.com/docs/user/manual/en/introduction/open-source