Indeed they are all system wide available. You can even have some application using more than one of the mysql services.
Php application aware of sockect are few, most of them will try to connect to a port, you have to find a way to define the one you want to use for your particular app. Some let you put it in a variable, some will just need you to add it after the hostname or ip (localhost:3306), some will just assume 3306 and just ignore anything else.
As a resumé mostly the answer to your question is :
- localhost:3306 or localhost to use the original mysql version
-localhost:3307 to use the mysql55 version
- localhost:3309 to use the mysql57 version
Where is the hell the 3308? I kept it for mysql56 in case i take time to adapt it.
Also: smeserver-mysql57 is an adaptation of smeserver-mysql55, it is still alpha as i did not have the time to fully test, should be fine, but would be happy to ear from you if you manage to test it before me .
Lastly: i think this piece of information and the one provided by mmccarn should be added to the wiki, as this could be a frequent question, what to do to use the one installation i want