Conradh na Gaeilge
The Conradh na Gaeilge, which translates to the Gaelic League, was never formally a nationalist party, however it fits into this realm of rebellion as it introduced and united many nationalists. The Gaelic League was founded in 1893 and is still relevant today as it is a non-governmental or political group that promotes the Irish language, Gaelic, throughout the Republic of Ireland as well as throughout the world. While the Gaelic League was not a political group organizing against Great Britain, it was still denouncing the use of the English language and implicitly stating that the Gaelic language was preferred and superior in Ireland.
In 1902, the America branch in New York published the book Rinnce na h-Eireann: A Simplified work on the Performance of the Dances of Ireland which taught how to do such traditional dances as the four-hand reel and "High Caul Cap", dances that schools worldwide still use at the show and competitive levels. The Gaelic League was responsible for the revival of culture and language and this example shows that it was to be revived not only in Ireland, but among the Irish-Americans, and also worldwide.
That being said, while the members were never outright political organizers, the Gaelic League unitentionally brought together many nationalists and republicans. Nationalists who were continuing to gather against Britain used language and culture to unite themselves and draw in more Irishmen and women. Many in Ireland beginning in the 19th century moved to have a revival of the Irish language and culture. These drives and movements led to the formation of groups such as the Gaelic League as well as the Gaelic Athletic League.