1/ A web-calculator which does more advanced functions. See http://live.sympy.org/#example and Sage Web Notebooks -- hell even google does quite a few things.
2/ A natural language science search thingie -- i.e. a smart algorithm which understands what data to shoot at you given your query. (query recognition ML? NLP?)
3/ An open source / community-editable platform for editing scripts for 2/.
I can imagine there are some interesting lessons about machine learning and NLP to be learned from such a project. In particular 3/ seems like a good thing to have in general: functional modules (transformations?) which take some input data and produce another type of data.
The components 1/, 2/ and 3/ above would work really well if restricted to a specific application domain. This way we would have a chance of competing with Wolfram and understand verbs from that domain + use structured data from dbpedia et al.
Very cool. pm me if you are working on any of the above. I would like to help.