The Society for the Promotion of Elfish Welfare (abbreviated to S.P.E.W.) is a society founded by Hermione Granger in 1994 aimed to improve the lives of house elves which attracted minimal interest. The other members of S.P.E.W. include Harry Potter and Ron Weasley.
Actions done to help the house elves and raise awareness of S.P.E.W. included Hermione knitting hats and other woolen items for the elves to find (often collected by Dobby) and going around Hogwarts with badges and 'harassing student in the corridors'.
Unfortunately, in Hermione's time at school, S.P.E.W. wasn't very successful. However, once she became Minister for Magic, Hermione made many key changes for non-human magical beings.