"Disjoint toolsets" vs. "disjointed toolsets"

Solution 1:

"Disjointed" is indeed the main adjective form of "disjoint," but mathematics is a special case. When outside the academic field, "disjointed" is used to describe something that is separated at the joints or dislocated. In mathematics, "disjoint" is used to describe sets with no elements in common. Essentially, the answer is it's simply a matter of convention.

See the definition for disjoint and disjointed.

Solution 2:

The concept of disjoint sets comes from the world of mathematics and has nothing to do with disjoint(ed) toolsets. If you take a look at the definitions of the two words, you'll see that disjoint as an adjective is now obsolete outside of this mathematical sense:

DISJOINT

1. obsolete : disjointed 1a
2. : having no elements in common <disjoint mathematical sets>

DISJOINTED

1. a : being thrown out of orderly function <a disjointed society>
   b : lacking coherence or orderly sequence <an incomplete and disjointed history>
2. : separated at or as if at the joint

So unless you're specifically talking about sets in a mathematical sense, I'd recommend:

There are disjointed toolsets all over the place…