Darknet is described as ': Open Source Neural Networks in C'. There are five alternatives to Darknet for Mac, Linux, Windows, Online / Web-based and Java. The best alternative is TensorFlow, which is both free and Open Source. Other great apps like Darknet are mlpack (Free, Open Source), Deeplearning4j (Free, Open Source), Cloud AutoML (Freemium) and MXNet (Free, Open Source).
TensorFlow is an open source software library for machine learning in various kinds of perceptual and language understanding tasks. It was originally developed by the Google and later released under the Apache 2.0 open source license on Nov 9, 2015.
mlpack is a C++ machine learning library with emphasis on scalability, speed, and ease-of-use. Its aim is to make machine learning possible for novice users by means of a simple, consistent API, while simultaneously exploiting C++ language features.
Eclipse Deeplearning4j is the first commercial-grade, open-source, distributed deep-learning library written for Java and Scala. Integrated with Hadoop and Apache Spark, DL4J brings AI to business environments for use on distributed GPUs and CPUs.