I probably should mention that IronPython is probably the ultimate example of alternative languages for the .NET framework.  It was developed first independently then in cooperation with Microsoft.  Microsoft made IronPython team member Jim Hugunin part of the CLR team.  Not a bad recruitment strategy, how many people can claim to have worked on porting a language to the .NET framework successfully.  IronPython seems to have all of the major .NET 2.0 features which Boo is still missing but Nemerle is way ahead on because Nemerle also has the C# 3.0 features. 

So IronPython looks pretty good if you're a Python fan.  I myself don't care for Python.  There is no particular reason to dislike Python, I'm sure it's a perfectly fine language.  I've played around with it a little bit but didn't find anything that convinced me that I needed to make Python part of my arsenal.  It's a nice enough scripting language along the lines of Ruby.  Which brings me to another point that I didn't mean to get to:  Languages seem to pick off the most converts from languages that are very similar.  For example, C# is about 95# Java and so someone who knows Java would feel at home in C#.  I think the same can be said very generally about Perl and Ruby but not to the same degree.  I think Python and Ruby are going to compete in the same niche but I don't really see the difference between them besides the syntactic niceties and some miscellaneous differences. 

I wonder if there is a biological law or principle about this?  I thought I remember learning about this at some point.  The principle is something like the individuals most like you will compete for the same resources.  Nursing kittens with compete with their litter mates for the limited resource of their mother's milk.  I think this is true for languages.  I come across some language projects that make me wonder why someone would want to do that.  What is reason someone would need another scripting language let alone another general purpose language (C, C++, Java --> C#,J#,J++,Visual Basic)?  One valid reason I can see is that it targets another platform like Unix or Windows or a mobile device or perhaps it offers some powerful language feature that can only be accomplished in a new language.  Or perhaps the old language is controlled by a competitor or some similar entity and simply extending it is not possible nor feasible. 

Many people complain (wrongly IMHO) about JavaScript.  I think it is a very elegant language once you understand how it works and what you want to do with it.  JavaScript (ECMAScript) was built for a new platform, the browser.  It also makes a fairly decent and powerful replacement for VBScript for Windows scripting using Windows Script Host (WSH).  So I see the point of that language.  But WTF is up with JScript.NET?  What is the point of this bastardization and castration of a perfectly good language?

Some languages like Java and Ruby had the intent of making Lispy features available to the Average Joe.  This may be blasphemy but I don't think Lisp is all that difficult to comprehend.  What is difficult to comprehend is all the hoops you have to jump through in Java, C#, etc to get quasi-Lispy stuff (see Reflection). 

So with IronPython we have another example of bringing an existing language to the framework instead of using that effort to get a better language for the .NET framework.  The more I think about it the more I think that Nemerle is a LFSP whereas something like C# is more of a safety language. 

The .NET framework and the CLR are powerful tools and a language like Nemerle shows us what is possible.  IronPython shows us what was possible ten years ago. 

Disclaimer:  I make my living writing mostly C# code at this point.  I have also made money with Java and Visual Basic in the past.  I have not made any money or with non-average languages...yet.