I have used the GarageBand app and it has some interesting combinations. The amps they have made up are ok, but I think if they were as dynamic as a real amp it would cause serious hearing loss. It sounds pretty good when you track with the automated instruments. The good or bad part is you have to have an iPhone or iPad to use it.
I also have AmpKit that has a few good sounds for free and a new App emailed me with an app I haven't used yet called PocketHz which is supposed to slow or speed up songs on your player for learning songs and difficult sections.
But, I suspect you are looking for a low volume solution for playing while Mom or Baby is sleeping
What I have been using are two parts to lower the volume, but not ruin the tone. I only have one amp with a Master Volume, so I picked up a Swart Night Light attenuator, which is actually pretty transparent if you use a short quality cable to the unit.
As most of you guys know I have 3 kids and a Wife that doesn't always sleep hard, so this setup was important to me. I also found running a fan outside the door of whom ever is sleeping makes the solution fool proof!
The second part is a cheap hunk of plastic, which you might be able to homegrow, called an Ampwedge. It is a rubber like wedge you put under the front of your amp to tilt the amp back so all the sound hits your ears and you can play really quiet. I even use it when I get to play loud as it makes it easy to hear yourself without getting into a volume war.
I was originally looking at a product that works like a sling to tip the amp back, but because my Swart's unusual design it wouldn't work. I also saw a few reviews that said you lose a lot of bass with that design which you do not lose with the AmpWedge.
Gunbarrel Guitars, Evidence Audio wires.