VaultSharp

VaultSharp is the .NET client library for HashiCorp Vault. Instead of making raw HTTP calls to Vault's API, you get typed methods and objects.

Apache 2.0, C#. Covers the full Vault API: secret engines (KV, Transit, PKI, databases), auth methods (AppRole, Token, LDAP, Kubernetes), and system operations. Supports both Vault Community and Enterprise features.

Fully free. This is a client library: no hosting, no service, no paid tier. NuGet install and use.

The catch: this is a niche library for a specific integration. You need HashiCorp Vault already running (which has its own cost and ops story). VaultSharp just makes talking to it from C# easier. If you're not in the .NET ecosystem, this isn't relevant. If you are, it's essentially the only maintained Vault client for C#, so the choice is this or raw HTTP. At, the community is small, don't expect instant answers to edge case questions.