Big Edit: Solved! Thanks to everyone who helped me with critical information about this very little thing that doesn't affect any of you in a direct way. I am very grateful.

Original post-------------------

Question for #electronics people, #engineer people, etc.: What are these used for?
These are labeled (FB marketplace pic) as Woods XFC-2001 0B micro-inverters. What kinds of applications do they have?

Edit: The internet search engines are eager to tell me what the brand and model of these are (which I already know), but I'm coming up short trying to find what they're used for.

Edit 2: Welp, since somebody has 4 of them for sale, $10 each, half an hour from my house, I guess I'll own four of them if all goes well :)

Edit 3: Guess who's got two thumbs (currently) and four micro-inverter VFDs! This guy!

#question #whatfor

@guyjantic I think they're variable frequency drives (VFDs). I worked near people who worked on them at Motortronics in the 90s. My understanding is they produce the AC at variable frequencies to drive motors at different speeds. I worked on a different product and never got into the details.
@cgervasi Thanks! That's more than I understood. I mean, I basically know what an inverter is, but that semi-knowledge wasn't helping me at all.