You might have already heard of the Gulabi Gang through the film of the same name. On their official website, they define themselves as:
Rural women in pink saris, wielding bamboo sticks in pursuit of social justice
They are essentially a large group of pink-sari-wearing, stick-wielding, female vigilantes who aim to curb violence against women. Which is damn awesome.
The Gulabi Gang began when Sampat Pal Devi (founder) witnessed a man beating his wife. Everybody else tried to pretend it wasn't happening, but Sampat Pal couldn't stand the sound of the woman's cries. She petitioned the man to stop, but instead he beat her too. The following day, Sampat Pal Devi returned with five other women and a big stick, and they kicked the guy's butt!
The news of this spread quickly and women began to come forward to ask Sampat Pal Devi to make more interventions--and also to join her team. She soon realised that the group needed a uniform and a name, and so the Gulabi Gang was born, with their uniform of a distinctive pink sari.
Sampat Pal taught her 'sisters' to fight. They continue to intervene in cases of domestic abuse and also protest women's issues. They have stopped a number of child marriages, protest against dowry and female illiteracy, and have forced the police to register cases of domestic violence.
Their work is not all about beating abusive men. On their website, their mission reveals that they aim to help women improve their basic skills, become economically secure, and develop confidence to stand against abuse. So basically, they are supporting women in getting one step closer to equality.
Since the formation of the Gulabi Gang, many other centres for the sisterhood have sprung up across India.
Official Website of Sampat Pal Devi - lots more information here :)