I would 100% recommend Mjolnir as an actively-developed Slate alternative. sdegutis has a solid history of writing great window management stuff.
The mjolnir community does have an actively developed fork though called hammerspoon. http://www.hammerspoon.org/
I would recommend either of them, but hammerspoon has a smoother onboarding process.
We'd love to get feedback about Hammerspoon, or suggestions for plugins we could add.
Feel free to drop by #hammerspoon on Freenode, or file issues at https://github.com/Hammerspoon/hammerspoon
I just checked https://github.com/sdegutis/mjolnir, and I don't see any mention of this, and the last commit was from November 15.