30 years ago I purchased a wobble blade for cutting dados. Back then I didn't have much money to spend on tools, AND I didn't want to invest in much more expensive stacking dado set because I knew I would not be using it that much. 
Well, over the years I ended up investing in stacking dado set, which I don't use that much, but it does work well, but I still love my old "Wobble Blade" for doing other things ...

Watch it on Youtube: https://youtu.be/ymctM5tUgaQ

It's harder to find wobble blades these days, except at garage sales, swap meets and second-hand stores. Every time I stumble across one, I have a good look at it and most of them are in great shape having had very little or even no use ... 

The way a wobble blade works is it has a wider single blade that is off-set and as it spins it carves out grove or dado with straight lines on either side.

Wobble Blade
Even when I first purchased my wobble blade, more experience woodworkers would poo-poo my wobble blade by telling me that the way the action works on a blade-like that, the wider the dado cut the deeper the cove at the bottom of the dado ... because "after all, the bottom of dado should be true and flat". I carried on using it regardless ... and with good results for many years, never really bothering about the "coving" it was generating at the bottom of the dado cut.

Wobble Dado Blade

Then more recently after I finally did purchase a stacking dado set ... one day I decided to see just how deluxe my new stacking dado set was when compared with my old wobble blade by making exact 3/4" dados with each blade.

Table saw wobble blade

To my astonishment, the wobble blade made little if ANY coving in the bottom of my dados, I expected an "easily visible" cove ... but no!  It is barely noticeable at all, and that is when using unforgiving 3/4" MDF, that shows every flaw for things like that. Sure ... a wobble wheel will make a coved bottom dado, but for 3/4" or even a bit wider it is negligible at best, which dispels the whole myth that using a wobble wheel dado blade is not an accurate way of cutting dados.

They can be a bit harder to set, but if you take your time and make your own marks as I did so you can reset the blade with precision accuracy every time.

Wobble Blade for the table saw
No matter, I still keep my wobble blade handy and use it for other things ... I love how it can cut very narrow dados, even narrower than my stacking dado, and cleaner too, which makes it great for inlay work. Because it's a dado blade, I can (if I want) even sharpen the teeth on that blade, it is very forgiving. I would NEVER even attempt to sharpen any of my expensive table saw blades, all that does is ruin the blade by making inaccurate angles on the teeth ... yes they are sharp, but they cut ragged. A sharp blade does not always equal a fine cutting, no tear-out blade.

Table saw blade Wobble wheel

And lastly, the wobble blade is one of the only blades you can use for cutting coves in wood and because you can vary the angle, you can get coves of varying width and depth .. and nice clean work, but you need to take your time ... and the blade needs to be sharp as well.  This kind of work cannot be done easily, it at all with stack dado set ... depending on what you need. Anything I have seen is very rough and basically unusable. You can use a full kerf ripping blade, but it's less than ideal and you need to make sure you take tiny cuts each time so it becomes quite tedious. 

Table saw blade wobble wheel insert

So ... if you don't have a wobble blade, it may be something you can use to make what are otherwise very hard cuts to make with other table saw blades. And if you invest in a used one, just make sure there are NO chipped teeth ... ANY blade with chipped teeth should be discarded because if there are chipped teeth the blade may have sustained a bump which means there could be invisible cracks in the carbide of any of the teeth which can and has ... flown off during the cutting and hit woodworkers in the face ... not worth the risk even with good eye protection for the sake of an otherwise inexpensive table saw blade.

Here is an example of a Wobble Blade available from the Woodworkweb Amazon Store