In this page Nat Friedman (of Gnome and Ximian fame) has created some really nice demos showing Beagle and Mono.
Mono is an OSS implmentation of Microsoft’s .Net platform. Nat has created two demos for Monodoc (the Mono documentation browser) and for creating GUIs with Glade and Gtk#.
Beagle is a cool OSS application written in C#. If I am correct, it currently runs on Linux using Gtk# and there is an ongoing effort to port it to Windows. Beagle is a desktop search tool. It indexes your data (doc, pdf, images, html,… files) and let’s you search them efficiently.
I really like the fact that Beagle integrates well with other desktop applications (mail, IM, photo albums,…) and that supports many file types. The coolest feature of Beagle is live incremental indexing of files. It indexes your files as you create them without having to rebuild its indexes. See it here in action.
Beagle is backed by DotLucene the .Net (C#) port of the fabulous Lucene text search engine library.