The Concept.  I was looking for a wrench storage rack for my tool cabinet and ran across a rather simple commercial product with a couple rails and separators that was, frankly, more than I was willing to pay even though I liked that it was adaptable and modular.  The fundamental principles involved, however, were pretty basic so I took a whack at designing my own rails and separators.  The reality is that the commercial system was probably injection molded from nylon or something and probably testing 9,000 different ways to comply with a bunch of commercial and military standards or whatever so it would be stronger than what I'm uploading.  That said, if you aren't wrenching professionally, throwing your tools in your drawer from across the room, or deeply invested in saving a couple microseconds when reaching for a wrench, this might be for you.  The basic idea is that there are spacers that slide onto rails with a snug fit and provide slots in which you can store your wrenches, offset wrenches, ratcheting wrenches, sockets, whatever. 

Spacers.  There are a couple models of spacers here:

1.  Spacers slanted at an angle so that you might see more of the side of the wrench where the size information is.  There are several photos of these.  The problem with these, if you will, is that if you are going to obsessively label thiings, a slanted surface isn't ideal.  I did use Bambu Studio to put a couple 10mm letters on the face of the slanted divider, but figured trying to print it in a separate color was going to generate an awful lot of waste.  That said, as you can see in another picture, taking a white paint marker and hitting the highlights of the letters that were printed in the same filament as the rest of the body works pretty well.  There are slots for two rails in the slanted spacers, so they work a lot like the commercial ones I saw, except, well, they are slanted.
2. Spacers that are straight up and down and have slots for two rails.  This is more or less how the commercial products work.  The fit is nice and easy if the spacers are printed “flat”, but that makes it difficult to apply a label where you can see it.  I did print some in a “tall” orientation with labels that came out fine w/o supports, but the slots for the rails are a bit messier and the fit is a lot tighter.  If someone really wants to, I think the answer would be to mod the rail slot to put a triangular “hat” on the top of the void that accommodates the circular part of the rail--that would probably print with less stringing, which is what $(*!)s up the fit.
3. Spacers that are straight up and down and have a single rail slot.  These are like (2) above, but half width.  They accommodate the more modular rail approach discussed below.  Again, printing flat makes a nice slip fit.  Printing tall lets you apply labels, but take more work to slide onto the rails.

Rails.  I've included 300mm, 100mm and 50mm rails.  As long as your spacers are in the right place, you can use the width of the spacer to  join rails together to make longer rails; hopefully the variations are enough to cover most needs.  I've also included a gridfinity 1x1 block that can serve as a rail endpoint if you want to incorporate this into a gridfinity setup.  The alternative is that the rails have press fit (strong press fit, like with a small hammer) for 10mm x 3mm magnets.  I've got a pad in the bottom of my toolbox drawer and they cling OK with the 10x3 magnets.  At least they won't slide around under normal use but they aren't going to be much good in, say, an earthquake.

Modular Rails.  As I was messing around with these, I realized you could make interlocking spacers to have different distances between the rails--the object I've labeled “Splice.”  One of these separates the rails by 50mm.  If you lock two splices together with a “Pin” (a 12mm long “rail”), you get 100mm separation.  You can see in a pic how it works.

Printing.  I printed these all in PLA with default Bambu Slicer settings because I'm basic.  Seems strong enough for my tools (you'll see a pretty freakin' large wrench in a lot of the pics--it's a 1 ½" wrench that is 18" long, weighs a ton, and seems to work with this stuff just fine (don't ask and no, I don't work on Mack Trucks).

Sockets, oops.  The commercial variant of these also has spacers for ¼", 3/8" and ½" sockets.  Pretty easy, I think, to do and I'll try to bodge some up and upload later.  

Fusion 360 Model.  I've included the Fusion 360 file for all these parts (you'll see I'm not a Fusion 360 guru, so the model is pretty messy) and you can roll your own socket spacers for the rails or whatever else.  I was messing around with the clearance between the “socket” for the rails and the rails themselves and tried 0.2mm of empty space between them…. and that was too much.  So was 0.1mm.  And 0.05mm.  I settled for nothing and it seems to work just the way I want--nice close fit.