I'm not sure. I'll throw out some recent ones I've seen. Fossil SCM tries to stay simple. All the separation kernels stay in around 3-10kloc range to enable high verification. QBE backend, a LLVM alternative, has that as a design goal. Might count Nanopass since they simplify the foundation with most of the rest optional based on cost/benefit. I was really impressed with lwan's claims . The Lua VM probably counts. IIRC, Yogthos or someone else told me the Clojure language itself was simple with libraries doing most of the work. Any number of resource-constrained, embedded works  such as lwIP .
 I think you really missed your calling doing processor optimization and web apps. Your hobby interests are a perfect fit for embedded, software development. Might have even gotten you more skill and equipment for the hobby. Check out Jack Ganssle's The Embedded Muse if you don't already. I don't understand a lot of it but what I do is cool as hell. Mental comparisons with it will make you laugh when SW folks say stuff like unikernels aren't debuggable. :)