Lady Blackbird is like a steampunk version of Firefly. It’s free and was written by the same guy who made blades in the dark! linky

I’ve been enjoying Connect, it has a RIF-like interface if that’s something that matters to you

I’ve had great luck with Marshall Miller’s dungeon starters— they used to be all over the internet but looks like the canonical Google drive source got taken down. Looks like there’s some backups here: https://rpggeek.com/rpgseries/22715/dungeon-starters. Several are also included in that 20 dungeon starters book that wunst mentioned, and I also highly recommend. I used a modified version of the Sky Chain as a dungeon in my first DW campaign and it worked great!

As a side note, it’s pretty trivial to convert over one-page dungeons (like those from competitions or the amazing Trilemma Adventures https://trilemma.com/ ) into dungeon starter-like prep. Good quality one-pagers tick all the same boxes as good dungeon starters— dripping with flavor, self-contained, and easy to drop in to most settings without much work.