I love Gridfinity but have been frustrated when I have a drawer or shelf with a small amount of unusable space left over. I've also needed custom size compartments in bins to accommodate tools, drill bits, and other hardware.
With these problems in mind, I've remixed @Seishin's OnShape parametric solution to allow bases and bins of any dimension and grid size to be created. You can add any amount of fill space on any side (or all sides) of bases and bins, and you can even create a custom grid size. These changes go beyond the Gridfinity spec, and while some folks may not like that, I like the extra degree of flexibility.
To get started: Go to my OnShape document (Fully customizable Gridfinity bin & base generator), make a copy and go. Click on the tabs on the bottom of the screen for simple Getting Started instructions.
You'll find the solution to be robust and polished. I've tested and fixed many edge cases, resulting in a user experience that feels predictable and reasonable. The model does a good job rendering whatever you ask it to do in a reasonable way. That said, I'm sure there are bugs, and I'll try to fix any that are reported.
l'm using OnShape because it's 100% free and has almost all the functionality I've used in Fusion3D. A big difference is that it runs entirely in your web browser, and while I found that weird at first, I've quickly become comfortable.
I've not uploaded a ton of pre-created models simply because there or too many possible combinations. If you would like something that meets your needs, and you're not ready to create an OnShape account, just add a comment, and I'll try to create what you want.
The author remixed this model.