Slingshield is a very interesting modification of Digishield.
There's a whitepaper here:
https://mega.co.nz/#!gBEQ3JhQ!0R40rMjdN8jbzxKAtH9X3ZciRx5yuBOsq7KWosGUFgo

But what I really like is the percentage-based-fees, because it works to solve the problem of securing the network as the block reward decreases.
This is a huge issue for Doge at the moment and I really wish they'd look at Fractal's take on things.

There was a bit of price hysteria when we switched over to slingshield but FRAC is still under most peoples radar.
The price has now returned to being extremely cheap but there's a lot less volume on the books, this means that it's very easy to push the price up or down.
I suspect that it won't take much interest to get the price moving up again, this time more solidly.

There are a lot of people who are really interested in FRAC's innovations and are holding medium-long term (myself included).
Everywhere I go I find that many people haven't looked into FRAC yet, but those who have really like it.