The current Legends client reportedly contains 409 slash commands, and a recent tool extracted them directly from the client tables. Rather than dump hundreds of obscure/debug-style entries that you will probably never use, here are the known player-useful commands, grouped by purpose.

Core character and movement commands
Command	What it does
/help	Shows available command help
/loc	Displays your current Y, X, Z coordinates
/target <name>	Targets a nearby NPC/player/corpse
/tar <name>	Short form of /target
/assist	Targets your current target's target
/assist <name>	Assists a specific player
/assist off	Prevents assist from automatically starting attack
/assist on	Enables attack-on-assist
/follow	Follows your current target
/follow <name>	Follows a named player
/stand	Stand up
/sit	Sit down
/camp	Camp to character select
/quit	Exit/camp command behavior depending on context
/rewind	Attempts to move you out of stuck geometry
/consider	Considers your target
/con	Common abbreviation for consider
/who	Lists players in your current zone
/who all	Searches across the server
/who <name>	Searches for a particular player
/who all friends	Shows online friends
/charinfo	Character/bind-related information
/surname <name>	Set/change surname when eligible

Legends specifically confirms /target works on mobs, players, and corpses within target range, and vertical distance does not count against that targeting range.

Combat
Command	What it does
/attack on	Start autoattack
/attack off	Stop autoattack
/assist	Assist current target
/doability <skill>	Activate a combat/general ability
/doability Bash	Example: Bash
/doability Slam	Example: Slam
/doability Taunt	Example: Taunt
/doability Kick	Example: Kick
/disc <name>	Activate a discipline/ability by name
/yell	Calls for help / unlocks the encounter for outside assistance
/autofire	Toggles automatic ranged attacks where applicable
/stopcast	Stops your current spell cast
/stopsong	Stops bard song
/stopdisc	Cancels/stops an applicable discipline
/shield <player>	Uses the shield ability where available

Legends supports ability names directly, such as /doability Bash; its current macro system also uses /disc <discipline name>.

For your Barbarian Warrior, these are particularly useful:

/attack on
/attack off
/assist
/doability Slam
/doability Taunt
/doability Cleave
Spell commands
Command	What it does
/cast 1	Cast spell gem 1
/cast 2	Cast gem 2, etc.
/memspellset <name>	Load a saved spell set
/memspellslot ...	Memorize/manage an individual spell slot
/book	Open spellbook where supported
/stopcast	Interrupt your current cast
/alt activate <#>	Activate an AA by ID
/tgb	Toggle targeted group buff behavior

Legends macro documentation explicitly confirms /cast, /memspellset, /memspellslot, and /alt activate.

Macro/social commands

These are extremely useful in Legends:

Command	Purpose
/hotbutton <name> <color> <text>	Creates a one-line macro hotbutton
/pause <#>	Delay in tenths of a second
/timer <#>	Adds a visual cooldown overlay to a macro
/doability <name>	Execute a skill
/cast <#>	Cast a spell gem
/disc <name>	Use discipline
/autoinventory	Put cursor item into first available inventory slot

An important quirk: in a macro such as

/pause 20, /cast 1

the /cast 1 happens first, then the two-second pause occurs. Legends documentation explicitly confirms this behavior.

You can also use substitution variables:

Variable	Expands to
%T	Current target's name
%S	Target subject pronoun
%O	Target object pronoun
%P	Target possessive pronoun
%R	Target race
%M	Your pet's name

For example:

/g Attacking %T!

Legends documents all six of those substitutions.

Communication
Command	Function
/say <text>	Local say
/s <text>	Short form where recognized
/tell <name> <text>	Private tell
/t <name> <text>	Short form of tell
/ttell <text>	Tell your current targeted player
/tt <text>	Short form of targeted tell
/gsay <text>	Group chat
/g <text>	Short group-chat form
/guildsay <text>	Guild chat
/gu <text>	Guild chat shortcut
/ooc <text>	Out-of-character chat
/shout <text>	Zone-wide shout
/auction <text>	Auction channel
/emote <text>	Custom emote
/reply	Reply to latest tell
/join <channel>	Join chat channel
/leave <channel>	Leave chat channel
/list	List joined channels
/autojoin ...	Configure channels to join automatically

EverQuest's chat system also allows numbered channels such as:

/1 Hello
/2 Hello

for whatever channel occupies that number. The standard EQ chat-channel syntax is documented historically and remains part of the Legends client command set.

Group and raid commands
Command	Function
/invite <name>	Invite player to your group
/disband	Leave/disband from group
/follow	Follow target
/assist	Assist target
/marknpc	Mark targets where supported
/xtarget	Extended-target commands
/xtarget save	Save Extended Target configuration
/yell	Open encounter to outside help

Legends specifically supports /xtarget save; recent Legends macro tooling uses it to establish tank, assist, and marked-target assignments.

Inventory and corpse commands
Command	Function
/autoinventory	Move cursor item into inventory
/hidecorpse all	Hide all corpses
/hidecorpse looted	Hide corpses you've already looted
/hidecorpse none	Restore corpse display
/loot	Loot targeted corpse where applicable
/destroy	Cursor-item destruction functionality depending on UI/client state

/autoinventory is especially useful in Legends macros and is explicitly documented by the Legends community.

Notes and quest tracking

You asked about this earlier, and one correction is worth emphasizing:

/notes

is the documented Legends command for keeping personal notes. The Legends wiki specifically recommends it for tracking classic quests.

Pet commands

These will matter a lot once you're using your Necromancer and later your Shaman pet.

Command	Effect
/pet attack	Attack your current target
/pet kill <name>	Attack a named target
/pet back off	Clear pet hate list and stop attacking
/pet follow me	Follow you
/pet guard me	Follow/guard master mode
/pet guard here	Stay at current location
/pet sit down	Sit
/pet taunt on	Enable pet taunt
/pet taunt off	Disable pet taunt
/pet taunt	Toggle taunt
/pet health	Print pet HP/buff information
/pet target	Target your own pet
/pet leader	Report the pet's owner
/pet get lost	Dismiss/kill your pet
/pet as you were	Reset some current pet orders
/pet hold	Hold mode; requires Companion's Discipline
/pet ghold	Greater Hold toggle
/pet ghold on	Enable Greater Hold
/pet ghold off	Disable Greater Hold

Those are directly documented for Legends.

For your Warrior/Shaman/Necro setup, you'll probably want a pet attack button such as:

/assist
/pet attack

and a panic button:

/pet back off
Bard commands

If you ever add Bard:

/melody ...
/queuemelody ...

Both are specifically mentioned in the Legends macro documentation.

Interface and convenience commands

Depending on the client/UI configuration, the Legends client command table also includes commands for things such as:

/map
/log
/loadskin
/loadspells
/loadsocials
/chatfontsize
/shownames
/showspelleffects
/filter
/key
/friend
/ignore
/anonymous
/roleplay
/inspect
/duel
/time
played