The BTCPay server is open-source code which enables entities to accept payments in Bitcoin. The project is relatively new and was launched in 2017. The server is compatible with the Bitpay API. The resource is free to use and is applicable mostly to merchants. The GitHub is relatively active with over 30 contributors and over 100 forks. One of the main selling points of the software is it enables merchants to accept payments with no fees. There are currently many merchant service providers which provide the same service and charge a hefty fee for their software. For example, companies which use BitPay to accept transactions will be charged a 1% fee on all accepted transactions. The mining fee for processing blockchain transactions is still applicable.
There is also support for a number of altcoins including Litecoin, Dogecoin, and Dash. The code also supports a number of key features on the Bitcoin network that a lot of other services do not have support for. These include Lightning Network, Segwit, and giving the user complete control over their private keys. Technical knowledge is required to implement the project. The documentation for implementation is available on the GitHub.