TabbyChat is an advanced program for Minecraft that adds tabs for chats and an API for adding messages. Additionally, it parses the content for channels and PMs, then separates them for easy access.

Interface

After opening chat, you will see that its functionality has changed drastically. Tabs will be located on the top and the text box will be at the bottom. By dragging the window you are able to move the chat. Right-clicking on a tab will open its settings. Alternatively, you may use the asterisk command. Closing a tab may be done by pressing shift or clicking the middle mouse.

Custom filters

It is worth mentioning the possibility to perform various actions when a chat message matches the defined Regular Expression via custom filters. These actions include the following:

highlight the matching text;
play a notification sound;
send the message to a specific or all tabs;
prevent the content from displaying.

Advantages

Among notable features of the mod it is necessary to point out the overhauled chat box, that you can move and resize. There are also message timestamps, spam prevention and spell-checking capabilities, as well as the ability to send multi-line outbound chat messages. Alternatively, you may try another Minecraft mod called 5zig.

Features

free to download and use;
compatible with modern Windows versions;
enables you to improve Minecraft chat functionality;
you can send multi-line messages, highlight text and more;
comes with spam prevention and spell-checking capabilities.