Hammerspoon is a programmable OS X automation and scripting tool. I use it for positioning windows using hot keys and in response to events (eg. plugging in or unplugging an external display, or launching an app).
Alas, Slate became abandonware. I continued to use it for a long time; if it ain’t broke, don’t fix it, right? Unfortunately, it was a little bit broken. I had a patch that fixed the main issue I was seeing, but at some point the app started silently crashing for me and I was never able to figure out why.
I looked into the obvious alternatives and was flabbergastered to see them flashing in and out of existence at an alarming rate. Steven Degutis alone has made half a dozen of them — AppGrid, Zephyros, Phoenix, Hydra, Penknife — before finally(?) settling on Mjolnir. Consider this insanely long list of window management tools for OS X. I didn’t want to have to rewrite my extensive Slate config (probably even into another language) if the tool I was targeting was not going to stick around.