BitCoinSharp is a direct port of the excellent BitCoinJ library. It implements the native BitCoin P2P protocol in C# for use in .net 3.5 and above. This library can be used to maintain a wallet and send/receive transactions without installing the official client. It comes with full documentation and includes an example application that demonstrates some of the more common uses.
$ dotnet add package BitCoinSharpNo README available.