QGIS indeed has this in the form of a Python interface you can use to write your own code:

https://docs.qgis.org/2.8/en/docs/user_manual/processing/scr...

The wonderful thing about the processing framework is how it gives bindings over several other GIS OSS tools like gdal.

In fact, you can run scripts developed using the Python interface without having to open the QGIS GUI at all. See the below gis.stackexchange question for a snippet on how to do this:

https://gis.stackexchange.com/questions/152762/error-algorit...