Two focus right now:

Building a working CAD software based on my own geometry kernel, Aetheris.

https://github.com/yuechen-li-dev/HeliosCAD

Since it's code based CAD for LLMs first and foremost, I'm trying to add visual programming into the UI, as well a new way of drafting that's closer to how mechanical engineers actually do sketching called IntelliDraft.

Other is the Concept programming language, as a successor language to C++, based off the idea of C++20 concepts, with templates, comptime, Einstein tensors, async/await, explicit state machines, CPU inference, Vulkan, easy C interop, and safety proofs built into the language itself.

https://github.com/yuechen-li-dev/Concept/

Currently still compiles to C11, self hosting is in progress and targeting AMD64 right now, but it'll be a while before finished since this is a difficult project even for frontier LLMs.