It's no secret that Dungeons and Dragons is having a major renaissance right now, thanks in part to the huge popularity of actual play streams like The Adventure Zone and Critical Role. Many more people are discovering or rediscovering tabletop roleplaying games and using homebrew and official content to flavor their campaigns. Wizards of the Coast has released a plethora of sourcebooks and adventures, and the homebrewing community is thriving, with lots of people sharing ideas on social media.
However, not every Dungeons and Dragons player shares the same tastes and interests, and every group has to decide how to balance combat, roleplay, dungeon crawling, and exploring according to what is most fun for the people involved. Beyond meting out those basic elements that make up every game, some people want to try something new beyond the classic medieval European fantasy-inspired setting of classic DnD.
Some people like genre-bending or exploring other regions in DnD inspired by places beyond medieval Europe, like in samurai-era Japan or the American Wild West. Others like bringing in other franchises from their favorite video games, and the more popular series have seen large-scale conversions, so here are some of the most ambitious and fleshed-out homebrew conversion projects for DnD 5e.
Star Wars 5e
Star Wars 5e, often abbreviated as SW5e, is one of the most detailed and developed conversions for Star Wars and DnD. It includes a ton of resources, including a redone DnD Player's Handbook with race support for Twi'leks, Wookies, and more, and ten reskinned classes. Some are familiar to vanilla DnD fans, like the Fighter and Monk, although they have a specific Star Wars focus. There are also other "books" available for free: Scum and Villainy, a guide to enemies and creatures for SW5e like Jawas and Imperial Guards; Starships of the Galaxy, a vehicle guide for those wanting to fly their own Millennium Falcon; and Wretched Hives, which provides cities, factions, gear, and items.
There are a ton more resources available on the SW5e website, including feat and background reskins and guides for DMs and players to homebrew their own Star Wars-themed content.
Dungeons and Destiny
Dungeons and Destiny, also known as D&Destiny, is a project that has grown to include a ton of passionate creators, all with the goal of crossing over DnD with the world of Destiny and Destiny 2. The project uses DnD's core rules but adds in nine new classes based off Destiny's lore, like the Gunslinger and Sunbreaker, and a weapon system rehaul. It also adds in the Technology skill and gives characters a Light level alongside their spellcasting ability. The resources are free due to copyright law, and according to Dungeons and Destiny's website, Bungie gave the fans its blessing as long as they stay within certain guidelines. The project supports itself with a Patreon that enables patrons to have pre-release content and join the playtest.
All the resources can be accessed on Dungeons and Destiny's website, and there is also contact information available if players have questions or feedback.
Unofficial Elder Scrolls TRPG
This conversion project is also called UESTRPG, and takes DnD 5e into the world of Tamriel for fans of The Elder Scrolls. Like many other conversion projects, the classes, races, and backgrounds are reskinned, and the birthsigns mechanic has been added in. The website notes that racial and birthsign bonuses make characters much more powerful even at level 1 than vanilla DnD characters usually are, which DMs should keep in mind when creating challenges. UESTRPG's resources are available for free throughout the website, and there's an option for players to download "books" via Dropbox with an optional donation. The books include Basic Rules, Enemies of Elsweyr, Monsters of Murkmire, Bestiary of Summerset, and Blessings and Curses.
The resources and Dropbox link are hosted on UESTRPG's website, and bookmarking the site is a good idea as the creators continue to update with more content, like stat blocks for Nixads and Liches.