Is there any good alternative for Keras library?
I can't say which is more efficient or easier but MXNet exists, has interfaces to most languages (python, scala, R, C++, perl, Julia), and the code looks fairly similar to keras.

https://mxnet.incubator.apache.org/

Another one that I've come across is caffe, mostly because people seem to share a lot of pre-trained nets in their model zoo.

http://caffe.berkeleyvision.org/

Update: I didn't see caffe 2 but I think this is quite separate to the original caffe.

Finally I've not fully had time to check out H2O's offering in deep water which is an alternative to Keras but still sits on top of TF/MXNet/Caffe