hi, a want to make my own commands system for for example using bank accounts, changing signs Text Messages, opening/closing doors, mail system etc etc. I can make it but there is one problem, if user will write for example ".mail Bajki hi, bajki. Whats up ?" in chat window, everybody can see it. Is there option to hide it ? is there an option to create my own commands (with syntax /command) in script files ?

To hide it, have give your system an NPC interface. So the player types '/talk mail bakji hi bakji'. This way you have a nice UI and you can quite easily use existing utility scripts (interface_builder.lua for interface control, and topic_list.lua to handle the command/message).

Re custom commands: I think there might be a core method intended for this purpose (object:SendCustomCommand()) but its undocumented and all the bits that do anything are old and #if 0d out of the server. IDK if this is because noone thought it worth the effort to reimplement or if it was specifically removed.

SendCustomCommand was from Crossfire python, used to send commands like "drawinfo 1 text" to the player's client. Presently not used in Daimonin.

Adding commands to the server core can be tricky and have unintended consequences.  Using existing commands (including scripting commands) with custom script functions where nothing comparable exists is the preferred method.  I recently made a server modification (in my stream) adding another gmaster rank.  It took several files including a header or 2.