On this very day Gutama Buddha teached the first ဓမ္မစကြာ or Dhammacakka (Pali) to five Disciples, ပဉ္စဝိဂီ ငါးဦး, after his attainment of Buddhahood. It also marks the beginning of the Buddhist Vassa where Buddhist monks retreat to quiet place for 3 months long meditation.
Waso robe weaving festival (မသိုးသင်္ကန်းရက်လုပ်ပွဲ) or competition take place during full moon day where participants must finish weaving the robe before dawn which is later donated to the Buddha image.
Dhammacakka Sūtra audio below

Myanmar Martyrs' Day. This day is to commemorate fallen national heroes General Aung San, Thakin Mya, U Ba Cho, Abdul Razek, U Ba Win, Mahn Ba Khaing, Sat San Tun, U Ohn Maung and Ko Htwe during their struggle for the independence of Burma from British. They were assassinated on the July 19th of 1947 at 10:37 am while holding a cabinet meeting. The assassination was said to be planned by Galon U Saw.