Resources to run Spelljammer today

tl;dr: since it looks like we are keeping the same aesthetic, re-use our old Spelljammer stuff, what was old is new again!

If you want something to whet your appetite while waiting for August here are resources to get your space-swashbuckling campaign off the ground today. The quick hack for Spelljammer is 'do a ship-based campaign, but in space' - we can break this down into 'what are my tricks for doing ship based campaigns well' and 'how do I generate interesting 'space' themed stuff'

All logos from Wizards, used to illustrate relation

The simplest version is hand-wave the travel, describe how the party arrive at their destinations in Wildspace and then get straight to the space-themed encounter table.

If you want to do this, I compiled links to online encounter tables from original Spelljammer.

More advanced, to make it feel really different to, say, a planar campaign or space-travel with a teleporting mage needs us to to two things:
1. Get the ship right
2. Wrap the campaign around it

You can get most of the ship-schematics from Spelljammer.org. We have retained the look of the setting so apart from a few different ship names, you can get stuck in today!

The ship itself is your single greatest showcase of the setting - the party will interact with it and the crew most. Whatever signature strangeness is going on in the setting, make sure it is happening on the ship - both through showcasing arcane technologies, having space-faring races on the crew and by setting adventures on board with wildspace monsters.

Generate at least a half-dozen of the crew as junior officers or just personalities to showcase aspects you want to foreground. A navigator who can answer setting questions, some locals who might offer a view on power-dynamics and conflicts, some muscle to back up the party or guard things while they leave the ship.

Plan for the extra mobility and power - the party can now fly and bring siege weapons to bear (or drop large rocks on problems) - castles in the open are less to be feared but caverns and dungeons are still scary as they negate these advantages.

Challenge the players on two scales - first where the capabilities of the ship need to be leveraged and second where the crew have to dismount and operate alone. A Spelljammer typically ran quite a light crew relative to its size if they were in Wildspace to minimise air consumption and they are less able to be left un-crewed similar to leaving a ship at anchor. Except for dire circumstances there are far fewer opportunities to do mass attacks with the crew in Spelljammer compared to standard nautical campaigns.

For the large scale, you need a ship-combat system. I can suggest the following ones which we have playtested in the past year. The linked table tests for each system give a sense of how they play, depending on the feel you want one of these should work.
5e - Aces High from Arcadia magazine - very light, very fast, no actual grid just 'altitude' - stripped down, high energy rules set, built for flyers and people on flying mounts.
OD&D (updated) - Calidar, available on Bruce Heards blog in sections, most complex because it has wind influencing movement and damage is not just hull points, you can knock out masts, weapons, kill crew and so on. Feels really age of sail in that direction matters, ships are big & tough. Also accommodates flying creatures as written. Written with OD&D in mind but with guidance on how to adapt it to whatever system you are using (3.5e, 5e).
3.5e - Shadow of the Spider Moon from Polygon #151 - 3e update of Spelljammer, chunky, tactical action, about the middle between Calidar and Aces High for crunch.
AD&D Spelljammer - the original - ships are very tough to kill, it all serves as a platform for adventurers to sling spells, fight boarding actions - 'fights to the death' take a lot longer in this, probably not to recommend unless you really want to go with the original.

For general advice Mythcreants does a nice breakdown of Six Tips for Running a Ship-Based Campaign and Skullsplitter Dice wrote up a DM’S guide to Aquatic and Seafaring campaigns which is also full of advice particularly for ship combat.

If you want some guidance on getting the flavour right I wrote "updating Spelljammer - how to live your best space swashbuckling life" - a sweep up of Spelljammer feedback and thoughts on how to avoid the possible pitfalls. Finally there are other alternatives on this list of fantasy space-faring resources / settings / systems.