Abst is Computational Algebra System written in pure Ruby.
gem install abst
require 'abst'
p Abst.gcd(42, 30) # => 6
p Abst.isqrt(115) # => 10 (floor of square root)
p Abst.fibonacci(100) # => 354224848179261915075 (100th Fibonacci number)
p Abst.factorize(1000) # => [[2, 3], [5, 3]]
p 10.factorial # => 3628800
p 10.C 2 # => 45 (combination)
# etc...