JavaScript is a good example. It wasn't the only web scripting language available, there was JScript and Java Applets and VBScript. JavaScript won and now it's ubiquitous.
I agree with your JScript and VBScript answers, but not Java applets.
And for an example of co-existence of competing languages, see javascript triggering flash/actionscript (e.g. for clipboard access) and vice-versa (e.g. for DOM access).
Both are somewhat dated examples, that is pre-HTML5.
JScript is simply Microsoft's name for its JavaScript implementation. Presumably to avoid Sun's ire.
The entire history of HTML up to and including HTML5. :-)
I was gonna say, i think of all the arguments one can make, this is pretty much the least viable :)
Once the web became mass-market, standards pretty much became a complete mishmash in every area.