Your 2) is by far the most important to me. Not only does it allow to learn about solutions I could repurpose and their used patterns; it can also give me that last missing piece I was looking for that blocked me from building something.

That said, I'm especially looking for software "written in Rust" because I know the build process is standardized. I may need some dependencies, but I know how the build will work (cargo build -> if at all, all build instructions are in build.rs). I compile all rust-based open projects myself, and I have yet to stumble over a non-binding-specific package that won't compile.