Gives you the ability to personalize your player model's look by placing objects and effects on yourself. You can go from putting just a hat on your head to creating an entire new player model. PAC can also work on vehicles or props.
You can wear your outfit on any server with PAC3 and everyone should be able to see it on you as long as they have the content you used. If you're using content from Episode 2 (which very few people have mounted) You can also load custom models (.obj) and textures (jpg and png) from URL.
By default, PAC3 is in basic mode. You can change this by going to options > enable advanced mode.
You should visit the wiki
if you're confused on how to use it.
If you're interested in the latest version you can find it here
or for svn clients
The git version is updated more often than the workshop version is, but may be unstable.
Before asking on how to do X please check if it's covered in the FAQs first!
If you're completely new to PAC check out the Beginners FAQ
If you know the basics check out the Intermediate FAQ
If you have an issue with pac3 please report it on github