Today is Raksha Bandhan (or Rakhi), the Indian holiday where sisters are supposed to tie a bracelet around their brothers 
as a symbol of sisterly devotion. The basics of the holiday are at Wikipedia:
The festival is marked by the tying of a rakhi, or holy thread by the sister on the wrist of her brother. The brother in return offers a gift to his sister and vows to look after her. The brother and sister traditionally feed each other sweets.
It is not necessary that the rakhi can be given only to a brother by birth; any male can be “adopted” as a brother by tying a rakhi on the person, whether they are cousins or a good friend. Indian history is replete with women asking for protection, through rakhi, from men who were neither their brothers, nor Hindus themselves. Rani Karnavati of Chittor sent a rakhi to the Mughal Emperor Humayun when she was threatened by Bahadur Shah of Mewar. Humayun abandoned an ongoing military campaign to ride to her rescue. (link)
Though the holiday is strongly associated with Hinduism, in my experience it is somewhat of a secularized, “cultural” holiday both in India and the diaspora, where other religious groups participate. (I’m not sure if it’s absolutely universal — do Indian Christians and Muslims celebrate Rakhi? Is there Rakhi in Bangladesh or Pakistan? Based on this article, the answer to the second question is maybe.) Indeed, these days, it isn’t surprising to see Rakhi designs that contain references to Indian and western superheroes (check out this cool Spiderman Rakhi), alongside the more traditional designs.
In Haryana, a group of women tied Rakhis around trees, as an environmental gesture. (“Her other brother is a tree,” one bystander quipped.) Apparently the best-selling brand of Rakhis (“Laloos”) in the state of Bihar are named after the current Railway Minister, Laloo Prasad Yadav. (“But these Rakhis are only available on the black market!” the same bystander wryly noted.) And Indian PM Manmohan Singh recognized the holiday in a typical fashion.
