Update IMPLEMENTATIONS.md

Author: jwalton

IMPLEMENTATIONS.md

@@ -49,6 +49,7 @@ These tools are not endorsed by the OAI.
 | Fusio | [github/apioo/fusio](https://github.com/apioo/fusio) | PHP, JavaScript | Build API endpoints based on OpenAPI 3
 | Modern | [github/modern-project/modern-ruby](https://github.com/modern-project/modern-ruby) | Ruby | OpenAPI 3-based Rack framework with automatic OAS generation and requests/response validation
 | Koa2-OAS3 | [github/OverSpeedIO/koa2-oas3](https://github.com/OverSpeedIO/koa2-oas3) | Node.js | OpenAPI 3 request validation middleware for Koa2 based apps.
+| Exegesis | [github/exegesis-js/exegesis](https://github.com/exegesis-js/exegesis) | Node.js | OpenAPI 3 server-side framework for express and other frameworks.
 
 #### Code Generators