I was surprised to realize that there is no pinned thread with a list of all the active playtest content on DDB (perhaps the UA forum would be a good place).

A few that I am aware of:

• [Edit2]https://www.dndbeyond.com/classes/barbarian#PathoftheWildSoulUA
• [Edit2]https://www.dndbeyond.com/classes/monk#WayoftheAstralSelfUA
• [Edit2]https://www.dndbeyond.com/classes/sorcerer#AberrantMindUA
• [Edit2]https://www.dndbeyond.com/classes/warlock#TheLurkerintheDeepUA
• [Edit2]https://www.dndbeyond.com/classes/bard#CollegeofEloquenceUA
• [Edit2]https://www.dndbeyond.com/classes/paladin#OathofHeroismUA
• [Edit2]https://www.dndbeyond.com/classes/cleric#TwilightDomainUA
• [Edit2]https://www.dndbeyond.com/classes/druid#CircleofWildfireUA
• [Edit2]https://www.dndbeyond.com/classes/wizard#OnomancyUA
• [Edit3]https://www.dndbeyond.com/classes/fighter#RuneKnightUA
• [Edit3]https://www.dndbeyond.com/classes/ranger#SwarmkeeperUA
• [Edit3]https://www.dndbeyond.com/classes/rogue#TheRevivedUA
• [Edit5]https://www.dndbeyond.com/classes/fighter#PsychicWarriorUA
• [Edit5]https://www.dndbeyond.com/classes/rogue#SoulknifeUA
• [Edit5]https://www.dndbeyond.com/classes/wizard#PsionicsUA
• [Edit5]https://www.dndbeyond.com/spells/mind-sliver-ua and other psionic spells
• [Edit6]https://www.dndbeyond.com/subclasses/path-of-the-beast-ua
• [Edit6]https://www.dndbeyond.com/subclasses/way-of-mercy-ua
• [Edit6]https://www.dndbeyond.com/subclasses/oath-of-the-watchers-ua
• [Edit6]https://www.dndbeyond.com/subclasses/the-noble-genie-ua

[Edit6]Still no centralized location to find a list of all active playtest on DDB (except here, but this is supposed to be a request).

Did I miss any?

Well there's

>] 4 elven subraces Aereni & Valenar (High/Wood), Kalashtar, Shifters, Warforged. Kinda miss the Viashino but the race didn't make it apparently.

>] all Dragonmark subraces and feats

>] of subclasses you only missed the Giant Soul Sorcerer

Quote from NeoPhantom >>

Well there's

>] 4 elven subraces Aereni & Valenar (High/Wood), Kalashtar, Shifters, Warforged. Kinda miss the Viashino but the race didn't make it apparently.

>] all Dragonmark subraces and feats

>] of subclasses you only missed the Giant Soul Sorcerer

 I already counted the races and dragonmarks from eberron.

I did miss giant soul though.

Edited for most recent wave of playtest subclasses.

I anticipate a fighter, ranger, and rogue UA in the future.

Quote from DxJxC >>

I anticipate a fighter, ranger, and rogue UA in the future.

 I called it (I'm sure a lot of people did) and edited them in.

I also found out the items of eberron are also playtest (I guess the only thing we bought in that book was the lore...)

Removed eberron content (it is official now, for better or worse) and archived subclasses (brute fighter and giant soul sorcerer):

• https://www.dndbeyond.com/classes/artificer
• https://www.dndbeyond.com/classes/fighter#Brute
• The races (and feats) of eberron.
• Magic items of eberron
• [Edit]https://www.dndbeyond.com/classes/sorcerer#GiantSoul

what about way of the soul knife monk?

Quote from SmarfMagoosh >>

what about way of the soul knife monk?

 Soul knife rogue actually. Thanks for reminding me.

Added 3 new psionic subclasses for fighter, rogue, and Wizard.

Fixed all the links (they added UA to the end of the URLs now).

Added psionic spells

Removed school of invention (I didnt forget it last time, it was still up...)

https://www.dndbeyond.com/classes/wizard#SchoolofInvention

I'm just bummed we still can't use the revised ranger class as a whole here on beyond, it makes the class super good!

Quote from SirRacha_ >>

I'm just bummed we still can't use the revised ranger class as a whole here on beyond, it makes the class super good!

 The revised ranger has been officially abandoned by WotC so it's not even in development. It's been largely replaced by the variant class features for the ranger in one of the more recent UAs

Added the "2020, part 1" UA subclasses and some personal exasperation.

It's beautiful. I'm so happy.

I hope you guys are better about updating it than I was of this (I was a few weeks (months?) late on some updates).

The barbarian should have 2 UA subclasses. The description is wild soul. The link is beast.

Shouldn't it be in the unearthed arcana forum?

Apologies if i'm missing something but it the UA CLASS FEATURE VARIANTS 11/04/2019 in here somewhere? Handy to be able to add things like additional fighting styles etc?

The Class Variant UA isn't currently on DnDbeyond. Its in development, but they've opted to not just implement a band-aid fix for them. It will be available eventually, but when it is it shouldn't cause problems for future content WotC adds because of the steps they're taking now. 

Ah ok, thanks for that, guess to utilise any of it id have to just do it manual at the table for now. Good to know its in the works.