Open-source full-text article recommendation engines

I'm wondering if there are any good .NET recommendation algorithms available in open source projects, whether attached to a search engine or not. By recommendation I mean something that accepts a full-text article and recommends other articles from its index based on keyword similarity.

At the high end there are document classification engines like Autonomy; at the low-end spam filters and blog "related posts" widgets. Possibly advertisement-to-article matching, too. I'd like to incorporate one into a project but can't afford the high end and the low end seems to all be LAMP-based.

[Sorry, one answer asked for clarification: What I'm looking for is ideally a standalone library, but I'm willing to adapt good source code as necessary. The end result is that I need to be able to create a C# service that accepts an arbitrary amount of text and returnsa list of similar previously-indexed articles. Basicallly, the exact thing that StackOverflow itself does as you are submitting a question!]

Thanks! Steve

From stackoverflow Steve Eisner

• Question is not very clear (algorithm or library???) but only thing that comes to mind is Lucene.NET, the porting of the popular Lucene library on the .Net framework. HTH.

  From massimogentilini

• I think that in StackOverflow they extract all common english words from the text and then compare this words with the remaining words of other posts to get the "Related" posts.

  From Eduardo Molteni