It's probably safe to say the final season of Game of Thrones didn't stick the landing for many of us, but HBO is pushing ahead on expanding George R.R. Martin's franchise nonetheless and are actively developing several spinoffs, including one that tackles the legendary journey of Princess Nymeria.
Deadline has reported that the project, known as 10,000 Ships, has found its writer has HBO as tapped Amanda Segel to write the potential series. The series will follow the "journey made by warrior queen Princess Nymeria and the surviving members of the Rhoynars, who traveled from Essos to Dorne following their defeat by the Valyrian Freehold in the Second Spice War." Amanda Segel has written for shows such as The Good Wife, Person of Interest, The Mist, and Helstrom, and is also developing a TV series based on Ubisoft's Skull & Bones.
In addition to 10,000 Ships, HBO is also working on 9 Voyages aka Sea Snake, which revolves around the great sea voyages made by Corlys Velaryon aboard the Sea Snake. Velaryon "journeyed to places including Pentos, Dragonstone and around the bottom of Westeros as well as to Lys, Tyrosh and Myr. He reached the fabled lands of Yi Ti and Leng, whose wealth doubled that of the House Velaryon, and him and the Ice Wolf headed north searching for passage around the top of Westeros, only to find frozen seas and icebergs as big as mountains." Rome co-creator Bruno Heller is developing the series along with George R.R. Martin. There's also another series set in Flea Bottom, the poorest slum district in King's Landing, as well as a possible adaptation of Tales of Dunk & Egg and an animated series for HBO Max. At the moment, the only Game of Thrones spinoff that's actually in production is House of the Dragon, which is based upon George R.R. Martin's Fire & Blood, a Targaryen history book which chronicles the history of House Targaryen, starting off with "Aegon the Conqueror, creator of the Iron Throne, and [going on] to recount the generations of Targaryens who fought to hold the throne, all the way up to the civil war, known as the Dance of the Dragons, that nearly tore their dynasty apart." The first season of House of the Dragon is expected to debut on HBO in 2022.