Initial sphinx-based documentation

docs/source/ecosystem.md

@@ -0,0 +1,85 @@
+# The PGPainless Ecosystem
+
+PGPainless consists of an ecosystem of different libraries and projects.
+
+The diagram below shows, how the different projects relate to one another.
+
+```{mermaid}
+flowchart LR
+    subgraph SOP-JAVA
+    sop-java-picocli-->sop-java
+    end
+    subgraph PGPAINLESS
+    pgpainless-sop-->pgpainless-core
+    pgpainless-sop-->sop-java
+    pgpainless-cli-->pgpainless-sop
+    pgpainless-cli-->sop-java-picocli
+    end
+    subgraph WKD-JAVA
+    wkd-java-cli-->wkd-java
+    wkd-test-suite-->wkd-java
+    wkd-test-suite-->pgpainless-core
+    end
+    subgraph CERT-D-JAVA
+    pgp-cert-d-java-->pgp-certificate-store
+    pgp-cert-d-java-jdbc-sqlite-lookup-->pgp-cert-d-java
+    end
+    subgraph CERT-D-PGPAINLESS
+    pgpainless-cert-d-->pgpainless-core
+    pgpainless-cert-d-->pgp-cert-d-java
+    pgpainless-cert-d-cli-->pgpainless-cert-d
+    pgpainless-cert-d-cli-->pgp-cert-d-java-jdbc-sqlite-lookup
+    end
+    subgraph VKS-JAVA
+    vks-java-cli-->vks-java
+    end
+    subgraph PGPEASY
+    pgpeasy-->pgpainless-cli
+    pgpeasy-->wkd-java-cli
+    pgpeasy-->vks-java-cli
+    pgpeasy-->pgpainless-cert-d-cli
+    end
+    wkd-java-cli-->pgpainless-cert-d
+    wkd-java-->pgp-certificate-store
+```
+
+## Libraries and Tools
+
+* {{ '[PGPainless](https://{}/pgpainless/pgpainless)'.format(repo_host) }}  
+  The main repository contains the following components:
+    * `pgpainless-core` - core implementation - powerful, yet easy to use OpenPGP API
+    * `pgpainless-sop` - super simple OpenPGP implementation. Drop-in for `sop-java`
+    * `pgpainless-cli` - SOP CLI implementation using PGPainless
+
+* {{ '[SOP-Java](https://{}/pgpainless/sop-java)'.format(repo_host) }}  
+  An API definition and CLI implementation of the [Stateless OpenPGP Protocol](https://datatracker.ietf.org/doc/draft-dkg-openpgp-stateless-cli/) (SOP).
+  Consumers of the SOP API can simply depend on `sop-java` and then switch out the backend as they wish.
+  Read more about the [SOP](sop) protocol here.
+    * `sop-java` - generic OpenPGP API definition
+    * `sop-java-picocli` - CLI frontend for `sop-java`
+
+* {{ '[WKD-Java](https://{}/pgpainless/wkd-java)'.format(repo_host) }}  
+  Implementation of the [Web Key Directory](https://www.ietf.org/archive/id/draft-koch-openpgp-webkey-service-13.html).
+    * `wkd-java` - generic WKD discovery implementation
+    * `wkd-java-cli` - CLI frontend for WKD discovery using PGPainless
+    * `wkd-test-suite` - Generator for test vectors for testing WKD implementations
+
+* {{ '[VKS-Java](https://{}/pgpainless/vks-java)'.format(repo_host) }}  
+  Client-side API for communicating with Verifying Key Servers, such as https://keys.openpgp.org/.
+    * `vks-java` - VKS client implementation
+    * `vks-java-cli` - CLI frontend for `vks-java`
+
+* {{ '[Cert-D-Java](https://{}/pgpainless/cert-d-java)'.format(repo_host) }}  
+  Implementations of the [Shared OpenPGP Certificate Directory specification](https://sequoia-pgp.gitlab.io/pgp-cert-d/).
+    * `pgp-certificate-store` - abstract definitions of OpenPGP certificate stores
+    * `pgp-cert-d-java` - implementation of `pgp-certificate-store` following the PGP-CERT-D spec
+    * `pgp-cert-d-java-jdbc-sqlite-lookup` - subkey lookup using sqlite database
+
+* {{ '[Cert-D-PGPainless](https://{}/pgpainless/cert-d-pgpainless)'.format(repo_host) }}  
+  Implementation of the [Shared OpenPGP Certificate Directory specification](https://sequoia-pgp.gitlab.io/pgp-cert-d/) using PGPainless.
+    * `pgpainless-cert-d` - PGPainless-based implementation of `pgp-cert-d-java`
+    * `pgpainless-cert-d-cli` - CLI frontend for `pgpainless-cert-d`
+
+* {{ '[PGPeasy](https://{}/pgpainless/pgpeasy)'.format(repo_host) }}  
+  Prototypical, comprehensive OpenPGP CLI application
+  * `pgpeasy` - CLI application