I don't have one at this time, but I'd like to know about their applications and uses. Where is a slew generator more useful than an envelope generator? How do people use them in ways that are useful and non-replicable via other ADSR/LFO/EG type modules? Thanks.

Three very simple use cases off the top of my head:

1) Sample and hold => slew => control CV

Rather than have an immediate jump when the sample and hold is triggered you will get a descent or ascent to the new value over your specified duration.

2) Bass drum => slew => inverter => compressor sidechain

The slew generator here will function as an "envelope follower" for the bass drum. When you invert that and pipe it into your compressor's sidechain input the compressor will make everything running through it quieter allowing your bassdrum (mixed elsewhere I think?) to boom in the mix.

3) Sequencer 1v/oct => slew => oscillator

You can use a slew generator here to create a portamento affect. Some slew generators have different values for up vs down, so you could have your portamento only appear as notes go up or alternatively if they go down, you could have different slew lengths up vs down, or you could dynamically gate and vary the slew length over time to have your portamento constantly changing.

There's way more possibilities than these three, but they're some simple examples I could think of.

A slew limiter takes an input signal and follows it, but at a delayed rate.

Square waves are excellent for showing what a slew limiter does. Visualize a really slow square wave that's two seconds long and 8volts... at the beginning it begins its positive cycle to +8volts and in the middle it dips down to -8volts. It's a nice long square wave.

Now for whatever reason, you don't want an actual square wave. Maybe its abrupt nature doesn't work for your needs. You need something that slopes. Enter slew limiter.

You can set the slew limiter to follow the square wave, but take time to get to the +8volt peak than its natural instant peak. The same can be said for the negative cycle. So the output looks more like a trapezoid than a square.

Slew generators tend to fall into two major categories. You have slew limiters that apply the same slope to both the positive and negative slope. You also have slew limiter that can act independently on the positive and negative slope.

Maths is a popular module that can be used as a dual slew limiter. It has many other functions. Plugging a signal into the input rather than trigger will get Maths to act as a slew limiter.

As far as usage. They can be applied anywhere you want to take a source signal and smooth out any changes in the signal. There's some blur between envelope generator and slew limiters. But an envelope generator is designed take a trigger (square wave) and act in accordance to its duration. If you're dealing with ONE trigger than the functionality will probably overlap. If you're dealing with a series of changes that never return to zero volts. The EG won't track properly.

Here's a great video Divkid does on the Joranalogue Contour 1 - Slew Limiter & Function Generator -- that should help!

It's also worth noting that the vaunted Maths is also based around slope gens, which are more or less slew limiters with CV over rise/fall in Make Noise's design. Plus, anything else based in the Serge "Universal Slope Generator" family fits this definition, too.