Vapor smoothing is relatively easy and works well with ABS using acetone.

* ABS gives off toxic fumes when printing, acetone is dangerous to breath, and flammable, so use in a well ventilated area, wear gloves and a respirator mask, keep the acetone away from a fire or heat source, use basic good sense!*

This only works on ABS with Acetone, there are other solvents for other filaments, but you start to get into controlled substances.

Polymaker makes a proprietary filament that smooths with IPA alcohol and is less harmful, a bit more expensive, they even make their own vapor smoothing chamber. I have yet to try it out, but would love to!
https://us.polymaker.com/product/poly...

See my previous post on printing ABS here:    • Successfully Print ABS on your 3D pri...  

Let me know if this was helpful and if you have any tips or tricks to add to this in the comments!