Had a similar one at my last role. It was a HTML5 remote desktop thing with websockets, TLS1.2 etc etc. Got a bug report from a user that it didn't work in Safari. We didn't have a Mac in the office to test with, so asked the user for more details.
"Oh no, this isn't a Mac, it's Windows"
This is a user of a highly secure system, containing user PII, who expected to use it on a 5 year old browser with XP.
The software used was a commercial tool made upon Guacamole (Apache) called Inuvika. It's pretty awful, but having Linux and Windows apps on the same virtual desktop is quite cool. I don't know how much of that functionality comes from Guacamole or from the Inuvika addons.
Inuvika/Guacamole also support plain RDP, but we didn't use this, just the html5 client (browser)
If you want to see what open-source can do then look at Guacamole and go from there.
"Oh no, this isn't a Mac, it's Windows"
This is a user of a highly secure system, containing user PII, who expected to use it on a 5 year old browser with XP.
~bangs head~