AMX Mod X has a wide array of scripting capabilities so people can write "plugins", or files which add on to a mod's functionality. It provides in-game administration tools, game statistics, server management and gameplay modificators. It is based on the original AMX Mod.
Plugins can take form in administrative services (adding new admin commands), statistics generation (StatsX), fun additions (godmode, etc), gameplay changes (WC3, CSDM), and much, much more!
You can also write modules to expand the functionality of AMX Mod X and add to the scripting language.
AMX Mod X and AMX Mod
AMX Mod X was originally based on AMX Mod, a similar Half-Life modification by OLO. However, AMX Mod began to slip into poor project policies (lack of public input, no open source enforcement, no central source code maintained, and much more).
Due to the dead appearance of the project as all maintainers had disappeared into oblivion, the AMX Mod X project was started.
Since then, the AMX Mod X project has come a long way. Nearly every portion of AMX Mod has been either rewritten from the ground up, cleaned up, or changed to work in a new system.
AMX Mod X is not AMX Mod. And better yet, it's almost fully backward compatible.