Free on Gumroad (https://pzaxr.gumroad.com/l/mcurve)

You can control a metaball with a curve, and manipulate it the same way you would a curve but for Meta Balls! :)

This is a addon, and the page will be constantly updated as new creations and documentation is made. 

Fun way to create with Metaballs, you can create all from one curve object, or multiple curve objects, using addition or negative booleans. 
MCurve, will make a valuable addition to your creation collection. :)

Update Log: 
Version 1.01 - Adjusted the settings for the empty mcontrol object instancing, and adjusted the placement for the MCurve Full setup.