Recently I developed 3 themes for Orchard Core CMS: Coming Soon, Freelancer, and Editorial. I used the Liquid Template Language to build the themes as opposed to the Razor Template Language which I have used for years and still use to develop custom themes and modules for Orchard CMS 1.x and custom ASP.NET MVC apps. Note that as of this blog post Orchard Core is only in beta 2, which means there can be breaking changes before RC for theme and module development. It's a little too early to talk details.
While sipping green tea at a local Starbucks today I developed an Orchard Core CMS Module to serve a robots.txt file that can be populated via the admin dashboard. This module makes me very nostalgic, because it was one of the first modules I developed many years ago when first learning how to develop modules for Orchard CMS 1.x. It was also one of the modules I later built as part of teaching Orchard CMS classes and giving presentations. It only makes sense that it is one of the first modules I develop for Orchard Core to help understand the differences in module development.
Turns out there is a fair amount of coding differences in developing modules for Orchard Core compared to Orchard CMS 1.x, but the concepts are the same. Experienced Orchard CMS developers shouldn't have too many issues transitioning to Orchard Core.
This is one of several modules I will be developing for fun before the official release of Orchard Core. In many cases I will be developing modules I built in the past for Orchard CMS 1.x and building them from scratch for Orchard Core to understand the differences.
If you want something developed in particular, let me know!