Shreddage Stratus is actually a Kontakt Library. So you’ll need Kontakt for it to work.
But the free version is so good, it deserves a spot on this list.
Shreddage 3 Stratus Free lets you add tons of nuance to a performance, making it sound more realistic.
For example, you can automate bite and vibrato or change the picking mode. And turn on “poly input” to convert the chords you play into voicings that would make more sense for guitar.
You can also choose between 30 different amp cabs. And swap between dynamic and condenser mics.
As far as distorted electric guitar goes, Shreddage is the best free option out there.