torchgfn: A PyTorch GFlowNet library

The increasing popularity of generative flow networks (GFlowNets or GFNs) is accompanied with a proliferation of code sources. This hinders the implementation of new features, such as training losses, that can readily be compared to existing ones, on a set of common environments. In addition to slowing down research in the field of GFlowNets, different code bases use different conventions, that might be confusing for newcomers. `torchgfn` is a library built on top of PyTorch, that aims at addressing both problems. It provides user with a simple API for environments, and useful abstractions for samplers and losses. Multiple examples are provided, replicating published results. The code is available in https://github.com/saleml/torchgfn.