This is an id tech 3 bsp entity editor. It can render opened bsp files with vertex colors, you can pick entities in the render with a simple click, you can edit the entity string, you can save the bsp file afterwards or choose to save as .ent file instead. The preview is updated when you click the button under the viewport.

W - Move camera forward
A - Move camera to the left
S - Move camera backwards
D - Move camera to the right
SPACE - Move camera upwards
C - Move camera downwards
LMC - Select Object under the cursor
RMC Hold and Drag - Rotate view
Mouse Scrolling - Move camera forwards or backwards
H - Hide currently selected entity
Alt-H - Unhide all entities
ESC - Deselect entity