Oxide
Oxide tools provide a framework for server-side scripting. You can download their API here, and start writing server mods for Hurtworld in C#, Javascript or Python!
For Oxide support and questions, see the Oxide forums.
Hurtworld SDK
The Hurtworld SDK is an official tool for creating custom content in Hurtworld. It currently supports custom Levels, simple networked objects, and custom Construction Packs. The SDK comes with a number of tools and frameworks to make creating mods easy.