I will collect here links to traditional music resources.
1. https://tanetskolomyykytainshe.org/ - folk dance sheet music
2. https://rysproject.com/ - Ukrainian traditional music, podcasts, video lectures (in Ukrainian)
3. https://www.polyphonyproject.com/uk - Ukrainian polyphonic songs, recordings and some information (in Ukrainian, English and Hungarian)
4. https://www.folklore.ee/ - Estonian folklore (Estonian, English, German and maybe Russian?)
5. https://musicatradicional.eu/es/home - traditional Spanish music (Spanish, Catalan, English)
6. http://www.maqamworld.com/en/index.php - a resource for Arabic maqam music
7. forum.chandrakantha.com - Indian music forum
8. rasikas.org/forums - Carnatic music forums
9. https://www.folk.ee/ - folk music events in Estonia
10. http://eestiviiul.rahvamuusika.ee/Karjase_lugu_238.htm - Estonian violín music (sheet music and recordings)
11. https://folkmusicbaltics.weebly.com/ - Estonian folk instruments textbooks
12. https://sites.google.com/view/pmteooria ... authuser=0 - traditional music theory (there doesn't seem to be much information on the website, but I'll use it to learn new Estonian vocabulary at least)
13. https://virbel.ee/oppematerjalid/ - Estonian traditional music learning resources
14. https://www.rahvamuusika.ee/?s=213
15. https://www.rahvamuusika.ee/index.php?s=4
These are all I can recall now.