One of the regular features at the D&D website is a monthly column entitled "Unearthed Arcana," in which the R&D group offers some new RPG material in draft form for players to experiment with in their own games. When I started putting more time into learning the Fifth Edition rules recently, I read through these articles to see what I might find useful for my own future games. The "Waterborne Adventures" installment in particular set me thinking again about using 5E with Freeport. So, with that in mind, here are some suggestions for using "Unearthed Arcana" material in that setting.
Eberron (2/2/2015): The changling race would make an excellent starting point for allowing civilized serpent people as a player character race: simply add Darkvision, and change Languages to Common and Valossan (with no third language).
The Artificer arcane tradition would also be a good fit for Freeport, both for members of the Wizard's Guild and independent enchanters. (My 3E Freeport games included one cleric/wizard PC who opened a magic shop when the campaign ended. She would translate beautifully to an artificer!)
This article also contains information on the shifter and warforged races, Action Points, and Dragonmark feats, which could be included in a Freeport game if the DM allows. For example, a warforged character's origin might tie into the background for "The Ironjack Legacy."
When Armies Clash (3/2/2015): Mass combat rules are unlikely to see much use in Freeport except in naval battles (which these rules do not cover), the occasional riot or gang war, or the sort of invasion scenario seen in Black Sails Over Freeport.
Modifying Classes (4/6/2015): This column expands on the brief guidelines on modifying classes and creating new classes that appear in the Dungeon Master's Guide. It provides two worked examples: a ranger variant with no spells, and the favored soul (converted from the 3E book Complete Divine) as a sorcerous origin. Either would be acceptable in Freeport.
Waterborne Adventures (5/4/2015): This article is full of material wonderfully suited to Freeport: the Mariner fighting style, the Swashbuckler archetype for rogues, and the Storm sorcerous origin. In addition, Freeport sees enough strange ships and crews pass through its waters that the minotaur race would not be out of place there. (After all, a minotaur captain does appear in one adventure, Dark Deeds in Freeport.)
The recent Sword Coast Adventurer's Guide includes an official Swashbuckler archetype, but I don't own that book to compare them. Likewise, I don't know how much other material from "Unearthed Arcana" (if any) that book contains (If any of my readers own it, please enlighten me in the comments!)
Variant Rules (6/8/2015): None of these rules is specific to any setting.
Awakened Mystic (7/6/2015): This psionic class has been updated and expanded to 10th level in "Psionics and the Mystic, Take 2," below (2/1/2016).
Modern Magic (8/3/2015): This installment deals exclusively with modern-day magic, so is not appropriate to Freeport.
Ranger (9/9/2015): A variant on the ranger class, which can be used instead of or alongside the Player's Handbook version. (See also "Modifying Classes," above [4/6/2015].)
Prestige Classes and Rune Magic (10/5/2015): Freeport attracts practitioners of all kinds of weird magical traditions, so rune magic would fit in just fine--particularly in the Wizards' Guild.
Light, Dark, Underdark! (11/2/2015): This article was designed as support for the Underdark-based Rage of Demons storyline, but all of it could be useful in (or below) Freeport: two new fighting styles (Close Quarters Shooter and Tunnel Fighter), the Deep Stalker ranger archetype, the Shadow sorcerous origin, and the Undying Light otherworldly patron.
That Old Black Magic (12/7/2015): Fiendish cults are a recurring problem in Freeport's history, so these conjuration spells are perfect for spellcasting villains. The Abyssal tiefling variant also fits in well.
Kits of Old (1/4/2016): The two new bard colleges (Swords and Satire) and the Scout fighter archetype are all suitable for Freeport. Mounted combatants are rare in Freeport, but fighters with the Cavalier archetype can be found here, too.
Psionics and the Mystic, Take 2 (2/1/2016): Psionics are quite rare in Freeport, but they are part of the distinctive flavor of the continent of Naranjan (detailed in Mindshadows), which is part of the greater World of Freeport. The Order of the Awakened can be used to convert 3E psions who specialized in powers based on mental ability scores. Use the Order of the Immortal for physical-oriented psions, as well as psychic warriors and soulknives. (Progression beyond 10th level will have to wait for a future "Unearthed Arcana" column, or an official psionics sourcebook.)
March 2016 Review (3/7/2016): This latest column reviews some of the best material being produced through Dungeon Master's Guild (the 5E version of the OGL), rather than offering new material itself.