Below are 3 easy to use tools for creating design files for simple laser cut boxes. These apps create the tabbed joints and even allow you to set the kerf amount for a better fit.
Boxmaker - A simple creation tool which outputs a PDF file. You'll need to open the PDF in Illustrator, add the designs to a template, and format the colors etc for laser cutting.
MakerCase - A more advanced tool which allows for extra features like t-slot joints, holes, and engraved text. The output is an SVG which you'll then need to open in Illustrator or Inskcape, add the designs to a template, and format the colors etc for laser cutting.
Tabbed box maker - An extension for Inkscape which allows you to create the design in Inkscape to streamline your workflow.