There is many commands available for you in-game. Here we will list what we feel are the more important ones.

General

/help
Views a list of available commands to you in-game.

/motd
Displays the login welcome message again.

/rules
Displays a link to the Rules.

/list
List all the players online. Also shows if they are AFK.
Communication
Private message
/msg <player> <message>
Sends a private message to a player that is online.

/r <message>
Replies a private message to last sender.
Mail
/mail read
Views all the mails send to you. You can receive mails even if you are offline.

/mail send <player> <message>
Sends a mail to a player. This works even if the player is offline.

/mail clear
Deletes all the mail on your inbox. If you get a lot of mail, clear it after reading because there is an inbox limit.
Other
/ignore <player>
Does not display any message from this player. It's the same command if you want to unignore.
Teleportation

/spawn
Teleport to main spawn area - Alma Castillo.

/back
Teleports you to your location prior to spawn or tpa.
Home
/home <id>
Teleport to your home. The id is set with the command below.

/sethome <id>
Set your home to your current location. Limit is 3 homes. The id can be any word you would like.

/delhome <id>
Removes a home. The id must match the one you choose with /sethome
Teleport
/tpa <player>
Request to teleport to specified player. They can accept or deny the request.

/tpahere <player>
Request a specified player to teleport to you. They can accept or deny the request.

/tpaccept
If someone wants to teleport to you or request for you to come, you accept with this command.

/tpdeny
Denies all kinds of teleport requests.
Personal

/afk
Put your character in AFK state. Also set automatic after 5 minutes inactivity. Notifies the server.

/balance
Display the amount of money you have.

/pay <player> <amount>
Pays another player from your balance.

/hat
Put on some cool new headgear.

/exp
View information about your exp.

/suicide
This command makes you kill yourself. Attention: Doing so will make you drop all items and lose the exp.

/me <message>
Describes an action in 3rd person. You egoist >.>

/nick <nickname>
Change your display name. Do /nick off to remove. Do NOT impersonate other players, abuse the command or put offensive words as nick.
Miscellaneous

/balancetop
View the top-list of the wealthiest on the server.

/recipe <name>
Shows you how to make a certain item in-game. e.g., /recipe chest

/itemdb (<name>)
View information of item in your hand, optional if you put a name after command. Short names can be used in trading as well.

/getpos
View your coordinates.

/compass
Describes your current bearing.

/depth
States current depth, relative to sea level.

/time
Display world time.

/ping
Pong! - Great for checking lag delays.