"If I had never dropped in on that single course in college, the Mac would have never had multiple typefaces or proportionally spaced fonts..."
This is a conditional sentence, some ESL teachers and some EFL books call it the third conditional.
if + past perfect, would / wouldn't have + past participle
In the main clause, let's omit the adverb never and replace it with not, “would not have had multiple typefaces (etc.)” the speaker is telling his audience had it not been for that single course, the Mac would have had fewer typefaces and less beautiful typography. But Steve Jobs did attend the course, and the first Mac did have multiple beautiful typefaces and proportionally spaced fonts, etc.
This type of construction is used to talk about the consequences or results of a hypothetical situation that did not occur. Because we cannot change what happened in the past, many grammarians call this conditional construction “unreal”
If I dropped in on that single course, the Mac would have many different typefaces. (the speaker is in the present, and is expressing a possible future consequence)
If I had dropped in on that single course, the Mac would have had many different typefaces or… (the speaker is explaining why the new Mac had only one typeface, and the spaces between the characters were all the same size)
(The OP's version)
If I hadn't dropped in on that single course, the Mac would not have many different typefaces or… (The Mac today has many beautiful typefaces (etc.) because the speaker attended that course)
If I hadn't dropped in on that single course, the Mac would not have had many different typefaces,…. (The first Mac had many different typefaces, etc. because the speaker did attend that single all-important course)
Only sentence 4 is the truth, and explains the consequences of a hypothetical situation in the past. When it was first introduced to the public the first Mac had many different typefaces and well-proportioned spaced fonts.