One of the best things about php (or LAMP) is that you can have multiple scripts on the same hosting account, so you can have a wordpress at /blog and mybb or phpbb at /forum and many other scripts residing on the same hosting account.
However lots of frameworks like ruby and php frameworks demand that you use the command line to start the server, unlike dropping a folder into an already running server. This means that you can’t run multiple scripts on the same server.
Why do many modern frameworks do this, where you start the framework by running it’s own server instead of simply uploading a folder into an already running server? Lots of web hosts don’t provide shell access, and it’s not suitable for many websites as some websites require multiple scripts.
You can host the apps on their own ports and use a file server like NGNIX or Apache to forward to the specific ports. You can run as many apps as you have available ports and resources.
Use a VPS like Digital Ocean, a cloud host like AWS, or a PaaS like Heroku, instead of a shared host.
You are mistaken. Frameworks, like Rails (Ruby is a language and not a framework) provide a server as a convenience but there is no requirement to use it.
ABSOLUTELY. A host is simply a server. It can (and does) run multiple applications.
Do not be confused by the fact that some (most) hosts will limit the number of domain names you direct to them.
And, remember, a “shared” host means you are just one renter in a large apartment building; sharing the water, electricity and use of the swimming pool with everyone else.