Machine Learning methods suited for CPU
With 12 or more CPU cores, you wan work with pretty much any deep learning model.  Only thing that will not work is training with 100k+ images or more than TBs of test.  For such scenarios; you can seed the model with transfer learning.

For example, training a Cat/Dog image classification model (from scratch) takes 2 hours on 6 core i5 (as compared to 30 minutes on GTX 1080ti).