We use Android/iOS Virtual Machines from appetize.io, you may visit their site to get paid VMs.
Retro Virtual Machines like Windows 1, 3, 95, 98 are hosted on our own server and do not impose any time limit, Windows 10 is hosted on this website.
We also used provide hosted sub-domains where you could host and make websites for free but due to spam, we had to sadly close it.
We do not force anyone to be using our website, it is just for making you life easier with these compiled list of Virtual Machines :').
Yes, In fact, We have made an entire page dedicated to this here.
Yes, we do have plans to add more operating systems but due to other systems requiring powerful servers, we haven't been able to do so...
Appetize.io provides Android/iOS VM to free users at 100 minutes per month and even this site uses appetize.io for Android/iOS VM.
distrotest.net provides you with all the linux operating systems for you to test before you install a linux on your PC.
browserling.com provides you with Windows Vista, Windows 7 VM for free for a limited amount of time (3 min) where you can test your website or see if a site is down or not.
Google Cloud also provides you with free Debian Based VM with shell access in it's compute engine without any credit card. once you register for cloud console and make a project, just click on "Activate Cloud Shell" option on top navigation bar.
Lambdatest provides with you a lot of virtual machines for free once you sign up using your email address. From Macs to Windows, They have got you covered.
BrowserStack provides you with almost all the devices that are currently existent in the word, from Samsung, OnePlus, Google Phones, to iOS devices and Windows and MAC VM with all web browsers...