Serious Editor 1 is the editor used for creating content in Serious Engine 1. It was created by Croteam.
Overview[]

Serious Modeler.
Serious Modeler is a tool included with Serious Sam 1. This tool lets one import a model from a 3D model creator such as Blender or 3DSMax and import it into the format Serious Engine 1 uses for models. From there, one can do things such as assign model bones to the model, create a script that tells the engine how to render and animate a model, test how the model would look with the engine's lighting system, add animations to a model and test them out in the tool, and create levels of depth for a model so that it doesnโt take up as much resources when viewed at range.
As with the level editor, one can import and export textures, such as reflective textures so that a model or wall texture can reflect the world around it. In addition, there is a tool that lets the user export a model's UV Map to see where a model's textures are positioned on the model.
SeriousSKA Studio[]
This editor was included with Serious Sam: The Second Encounter. This editor creates skeletons in the bone format created for The Second Encounter. It basically serves as a replacement for Serious Modeler's skeleton and bone-creating tools.
Notes[]
The original release of Serious Editor 1 does not work on 64-bit operating systems. The Windows architecture used for Serious Editor is no longer supported by Microsoft, which makes it impossible to create or load a level or import a model into the model format Serious Engine 1 uses. You can use a 32-bit operating system, such as Windows XP or the 32 bit versions of Window Vista or Windows 7. This, however, is not recommended.
As of 2015, the Steam version of the game (titled Serious Sam Classic: The First Encounter) comes with updated executables of the editor tools, including 64-bit support for modern opearting systems. This is not true for the GOG version of the game, however, the editor executables are interchangeable without issues.[1]
The editor included with Serious Sam Classics: Revolution is compatible with modern OSes as well.