ATM I'm looking for bugs I can address with either TLA+[1] (hello concurrency) or Alloy[2] (hello design exploration).

Other times I had some linear algebra stuff I was working on, so I learned a bit of Octave[3] to generate test cases with a (hopefully) correct implementation.

I'm still looking for opportunities to try Z3[4] though... (e.g. http://phrack.org/issues/69/4.html#article see "How I Cheat at Maths - Z3 101").

1: https://lamport.azurewebsites.net/tla/tla.html

2: https://alloytools.org/

3: https://www.gnu.org/software/octave/index

4: https://github.com/z3prover/z3