What are the cool things that people create in the RO Development side?

I want to know more about what people create in the RO private server community and develop in their free or paid time. There is a lot of diversity in the content created by people and I've had a few people discuss the variety of creations with me. There are server projects that are making a huge amount of custom changes in the client side. That is very new to me as I'm focused more on the server side. I want to know more and I know that the industry staff will be able to comment or educate me on the differences and the variety of projects that accustom changes which are new and innovative in the RO professional world. Thanks for answering and would love to hear more feedback. Thanks <3 Sephus.