Leatrix Plus is an efficient and modular addon which offers lots of quality of life improvements to enhance the default user interface in Classic. Leatrix Plus is available for Shadowlands, Burning Crusade Classic and World of Warcraft Classic.
Click the minimap button or enter /ltp to open Leatrix Plus. Some options have little configuration buttons next to them for further configuration. For a list of slash commands, enter /ltp help. If you're looking for map enhancement, there is now a standalone addon called Leatrix Maps (Classic).
Automate quests - Automatically select, accept and turn-in quests. Quests which have a gold requirement are excluded automatically.
Automate gossip - Automatically select a single gossip option by holding down the alt key when opening a gossip window. Banker, taxi, trainer and vendor gossip windows are automatically skipped with no alt key requirement.
Accept summon - Automatically accept summon requests.
Accept resurrect - Automatically accept non-combat resurrection requests.
Release in PvP - Release automatically after you die in a battleground.
Sell junk automatically - Sell all grey items in your bags when you talk to a merchant.
Repair automatically - Repair your armor automatically when you talk to a repair merchant.
Block duels - Block duel requests from people who are not friends or guild members.
Block party invites - Block party invite requests from people who are not friends or guild members.
Block friend requests - Block BattleTag and Real ID friend requests.
Party from friends - Automatically accept party invitations from friends or guild members.
Invite from whispers - Automatically invite someone to a group when they whisper a keyword of your choice to you.
Use easy resizing - Resize the chat frame upwards simply by dragging it.
Hide the combat log - Hide the combat log to make more room for chat windows.
Hide chat buttons - Hide the chat buttons to gain screen space.
Unclamp chat frame - Move the chat frame to the very edge of the screen.
Move editbox to top - Move the editbox to the top of the chat frame.
Disable sticky chat - Disable sticky chat so you can switch between group chat and whispers easily.
Use arrow keys in chat - Use the arrow keys to navigate the editbox.
Disable chat fade - Prevent chat text from fading.
Universal group color - Make raid chat text the same color as party chat text.
Use class colors in chat - Show character names in class color in the chat window.
Recent chat window - Open recent chat history in a copy-friendly window.
Increase chat history - Increase chat history from 128 lines to 4096 lines.
Hide error messages - Hide error messages shown in the error frame (with exclusions for a few important errors).
Hide portrait numbers - Hide the damage and healing numbers shown in the portrait and pet frames.
Hide zone text - Hide zone text (such as 'Ironforge').
Resize mail text - Resize text in the mail frame.
Resize quest text - Resize text in the quest detail frame.
Resize book text - Resize text in the book frame.
Enhance minimap - Rescale the minimap, hide zone information and use the mousewheel to zoom.
Enhance tooltip - Move, rescale and color the tooltip and show the unit's guild, rank (if same guild) and target.
Enhance dressup - Add tabard and nude buttons and hide the character controls.
Enhance quest log - Make the quest log frame double wide and show quest levels.
Enhance professions - Make the professions frame double wide.
Enhance trainers - Make the trainer frame double-wide.
Show volume slider - Add a useful volume control to the character sheet.
Show auction controls - Add controls to the auction house frame to speed up creating auctions.
Show cooldowns - Show up to five beneficial cooldown icons (of your choice) above the target frame or player frame for easy cooldown tracking.
Show durability status - Show itemised durability status in the character sheet and show an overall percentage after you die.
Show vanity controls - Show helm and cloak toggle checkboxes on the character sheet.
Show bag search box - Show a bag search box in the backpack frame and bank frame.
Show free bag slots - Show the number of free bag slots.
Show raid button - Move the raid frame toggle button so that you can toggle the raid container frame without opening the raid management frame.
Show player chain - Show a rare, elite or rare elite chain around the player frame.
Show Wowhead links - Show Wowhead links in the quest log frame.
Manage frames - Move and rescale the player frame, target frame and mirror timer bar frame.
Manage buffs - Move and rescale buff frame.
Manage widget - Move and rescale the widget frame (commonly used for PvP scores).
Class colored frames - Show the player and target frame backgrounds in class color.
Class icon portraits - Show class icons in the portrait frames.
Hide gryphons - Hide the gryphons shown either side of the main bar.
Hide stance bar - Hide the stance bar.
Graphics and sound
Disable screen glow - Disable the screen glow to reduce nausea.
Disable screen effects - Disable the grey screen of death and the netherworld effect.
Set weather density - Set the density of weather effects.
Max camera zoom - Increase the maximum camera distance to get a bigger view of the action.
Enable viewport - Show customisable borders around the game world with optional screen resize and transparency.
Silence rested emotes - Automatically toggle emote sounds when you enter and exit rested state.
Disable bag automation - Prevent your bags from opening or closing automatically when you interact with a merchant, bank or mailbox.
Show character addons - Sort the addon list according to character by default.
Disable loot warnings - Hide the warnings that appear when you choose a loot roll option or attempt to sell or mail a tradable item.
Faster looting - Loot creatures significantly faster.
Faster movie skip - Cancel cinematics without being prompted for confirmation.
Stand and dismount - Automatically stand or dismount when an action is prevented because you are seated or mounted.
Show vendor price - Show the vendor price in item tooltips.
Combat plates - Show nameplates automatically when combat starts.
Easy item destroy - Destroy superior items without the need to type delete and show links in all item destroy windows.
Media player - All of the game music tracks and playable cinematics in an easy to use, categorised and searchable media library.