My current project is my favorite. It's health care related, so I can't provide a link. However, it's a case and disease management system that lets nurses work with chronically ill patients to help them manage their diseases and hopefully have good results (not always possible, sadly.)
Ground up, green field development. I should say, WAS my favorite. Nowadays, no more innovation. It's all about adding features to meet requirements of external entities. But still, quite proud of it.
I'm the sole developer. I have a nurse counterpart who I work with very closely during development. She's a primary user of the system and the main source of feature requests (though not the only one).
This project includes many things I've never done before:
This project continues to challenge me in many ways.