To be fair, custom matchers in rspec are pretty easy as is: create a class that implements a few methods and then define a method to wrap that class.

Taking that one step further, with this simple script you can define your own custom matchers with a one liner:
matcher(:be_even) {|number| number % 2 == 0} matcher(:be_divisible_by) {|n, d| n % d == 0}