Add some extra comparisons to the readme (#2768)

Co-authored-by: James Hodgkinson <james@terminaloutcomes.com>

README.md

@@ -143,6 +143,35 @@ elements in a simpler and correct way out of the box in comparison.
 
 </details>
 
+<details>
+  <summary>Rauthy</summary>
+
+Rauthy is a minimal OIDC provider. It supports WebAuthn just like Kanidm - they actually use our library
+for it!
+
+Rauthy only provides support for OIDC and so is unable to support other use cases like RADIUS and
+unix authentication.
+
+If you need a minimal OIDC only provider, Rauthy is an excellent choice. If you need more features
+then Kanidm will support those.
+
+</details>
+
+<details>
+  <summary>Authentik / Authelia / Zitadel</summary>
+
+Authentik is an IDM provider written in Python and, Authelia and Zitadel are written in Go.
+all similar to Kanidm in the features it offers but notably all have weaker support for
+unix authentication and do not support the same level of authentication policy as Kanidm. Notably,
+all are missing WebAuthn Attestation.
+
+All three use an external SQL server such as PostgreSQL. This can create a potential single source
+of failure and performance limitation compared to Kanidm which opted to write our own high
+performance database and replication system instead based on our experience with enterprise
+LDAP servers.
+
+</details>
+
 ## Developer Getting Started
 
 If you want to contribute to Kanidm there is a getting started [guide for developers]. IDM is a