Gridfinity M.2 Holder. None of the currently existing models held enough drives so I made one that can hold more. There is a bit of wiggle to account for variations in drive thickness. There are currently 2 sizes, a half heigh and full height.  The Gridfinity dimensions are 3x1x3 and 3x1x6.

Update:

There is now a V2 that can hold up to 14 M.2s instead of only 7. Big thanks to @Nanianmichaels suggestion to use the free space on the ends to slots for smaller drives to be held vertically. There is a version for both heights now available.