Welcome to the forum!
There is no formal, standardize catechism like the CCC. However, many Church Fathers have written catechisms, both ancient and modern. St. Philaret's Catechism linked above is a great modern resource.
As far as more ancient sources, St. Cyril of Jerusalem, a 4th century saint, has his Catechetical Lectures
, which can be found both at the Christian Classics Ethereal Library
and New Advent
I believe that the RCC recognizes St. Cyril as a Doctor of the Church.