Some small additions/comments to an article by Kevin Newton "Ruby operators"

% - The modulo operator. This is usually only found on numeric types.

And Ranges :)

(1..30) % 5
# => ((1..30).%(5)) -- an ArithmeticSequence

!= - The inequality operator. This is found on almost all types, and is used to check basic inequality.

Maybe deserves mentioning that it can be defined individually or, if not, (like !~) breaks down to negating ==.

=== - The case equality operator. This method is used as the backend for case statements.

Also grep and any?/all?/none?.

[] - The element reference operator.

Maybe these usages deserve mentioning:

• Array::[]
• Proc#[]

Truthiness operators

My favorite pet peeve :) (1, 2)

I believe they deserve splitting into "boolean arithmetics" operators (&&/||) and "control flow" operators (and/or), and I don't think the latter deserve being described as "alias with no difference," as they have completely different precedence, and (as you most probably know :)) in allowed to use by parser in different contexts:

# allowed
foo = fetch_foo or return
@error = find_error and raise

# not allowed
foo = fetch_foo || return
@error = find_error && raise

(I believe "control flow and/or" were inherited from Perl.)

I would honestly say that &&/|| deserve to be in their own section (boolean math), while and/or's deserved place in this "Control flow" section.

Also, it seems like case is missing from "Conditional operators" section, or you don't consider it an "operator" (unlike if; I am not sure if the if and friends should be treated as "opertors" either, though).