Wildjammer - More Adventures in Space

Much in the spirit of fifth edition, this supplement is a recreation of Spelljammer mechanics, with a special focus on revising the 5e vehicular combat system. While much of the original Spelljammer lore is preserved, there are also some homebrew elements that help fill out the lore and gameplay mechanics to help it be more palatable to a 5e audience.

Files: Dropbox with a Collection of Materials
Foundry Module: Foundry VTT Module
Source: SurrealSage

Spelljammer Combat Expanded

The new official 5e ruleset for combat is pretty thin by many people's standards. For those that want to augment the system with additional combat choices, including player character ship roles, rules for skill checks, and additional stats for ships, then this is a great choice. It's pay what you want on the DMs Guild.

Files: Spelljamer Combat Expanded (DMs Guild Link)
Source: u/apopc7

Large Luigi's Guide to Space Monsters

It's still a work in progress, but this a community driven conversion of old Spelljammer monsters to 5e led by Fairyjars. It's worth checking back periodically on this effort to get updates to the bestiary and is unequivically the more comprehensive than effort for 5e monster conversions I've seen so far.

Files: PDF (54 MB)
Source: Hombrewery

One Page Spelljamming Adventure Generator

An incredible nifty ruleset for generating adventures in space that is RPG system agnostic, a few dice roles and you have have yourself the skeleton of a ready made adenture. John Huges, of the Blog of Holding, describes his process for developing this system.

D&D in Space - One Page Rules (450 KB PDF)
D&D in Space - One Page Rules (524 KB PNG)
Source: Blog of Holding

Simplified Spelljammer 5e Conversion

Jorphdan (the "ph" is silent) pulled together a bunch of disperate rules from a handful of 5e modules with a healthy mix of classic 2e. The video above gives a good sense of the ruleset and I've included the link to the document he mentions below. If this isn't enough for you, the rulesets just below this one are also excellent options.

Files: 5e Rules Conversion (Google Doc)
Source: JorPhdan

Spelljammer 5e Conversion (for theater of the mind)

The supplement updates spelljammer combat rules to 5th edition. Inspired by Starfinder and Esper Genesis, the rules provide a new way to manage spelljammer combat, streamlining the hex grid system into a quicker "theater of the mind" playstyle.

Files: Spelljammer 5e "Theater of the Mind" Ship Combat Rules (2.8MB PDF)
Source: Mike Hammock of the Tales from the Glass Guarded World Podcast

Spelljammer - Return To The Void

Take the classic Spelljammer setting and fast forward nearly 600 years where technology and magic are more deeply blended into an incredible 5e grounded campaign setting and ruleset. This one is very much worth your time, the art and the world is incredible. NOTE: There are a few pages missing and, if anyone finds a complete version, please send it to me.

Files (unfinished conversion): Spelljammer - Return To The Void (50 MB PDF)
Source: David Godinez

Spelljammer 5e Conversions (for hex grid)

There are two options here, both trying to be faithful to AD&D 2nd Edition rulesets. The first is unfinished and abandoned but feels quite polished with images and community feedback. The second is much denser and completed. If I were to focus on grid play I would use Trickishwheat8's rules, but there are a few different feats worth looking at in the older conversion.

Files (unfinished conversion):
36 Page 5e Rules Conversion (Unifinished) (32MB PDF)
GM Binder Source Code (Link to Github)
Source: Ubiquity4321

Files (finished conversion):
64 Page 5e Rules Conversion (746 KB PDF)
Ship Template Excel Sheet (39 KB XLSM)
Additional Resources from Trickishwheat
Source: Trickishwheat8

Homebrew Races

Solid 5th edition takes on some classic Spelljammer races. Kame Bit's goal is balance without sacrificing flavor. For example, the Exiled Illithid has feats they can take to gain the same skills as the version in the Monster Manual.

Giff (1.6KB PDF)
Dohwar (1.3KB PDF)
Exiled Illithid (2.6KB PDF)
Source: Kame Bit

Spelljammer Ship Sheet

A Spelljammer Ship Sheet that is compatible with the module Ghost of Saltmarsh 5e ship rules.

Files: Ship Sheet (452 KB PNG)
Source: coolfella69