BTCPay Server is a self-hosted, open-source cryptocurrency payment processor for Bitcoin. It also allows to add other crypto currencies like Litecoin, Monero.
But is there a similar open-source project for Ethereum and ERC20 crypto currencies?
BTCPayServer's implementation for ethereum never really worked and it was removed. I am the developer of Hub20, which aims to be a self-hosted payment gateway for Ethereum (and compatible chains). It also provides support for any scaling solution that is compatible with Ethereum's RPC API (Arbitrum, Optimism, Polygon, xDAI-Gnosis, etc) and it integrates with Raiden, which is Ethereum's analog to BTC Lightning.
Support for Ethereum and ERC-20 tokens were added in BTCPay Server in Sep 2020 https://github.com/btcpayserver/btcpayserver/pull/1730