In 2004, in response to an Australian law defining marriage as between a man and a woman only, a group of activists declared independence and raised a rainbow flag over the Coral Sea Islands.

Most micronations are vanity projects, attempts by individuals to exploit loopholes and legal grey areas in order to break free of the main (to paraphrase John Donne). The Gay and Lesbian Kingdom of the Coral Sea Islands is not one of those micronations.
Back in 2004, the Australian government explicitly forbade same-sex marriage. Federal law defined marriage as a “union of a man and a woman to the exclusion of all others.” That meant overseas marriages wouldn’t be recognised, and local gay and lesbian couples were completely shut out.
A flurry of amendments and attempts at repeal followed. But some activists took a different tack. They founded a kingdom.
June 14, 2004, a ship named the Gayflower landed on Cato Island. One of the Coral Sea Islands, Cato Island is a little outcropping on the southern part of the Great Barrier Reef. It’s uninhabited and populated mainly by birds… at least, until the Gayflower arrived. The protesters seceded from Australia, declared independence, and became the Gay and Lesbian Kingdom of the Coral Sea Islands.
The protesters camped out on Cato Island, now the nation’s capital city. They raised the rainbow flag, printed stamps, and declared war on Australia. Sure, this is all symbolic… but what a symbol!
The Australian government eventually came to its senses and passed the Marriage Amendment (Definition and Religious Freedoms) Act 2017. This legalised gay marriage throughout the country, and the kingdom officially rejoined their parent country.
[Thanks to David S.]