Gem/plugin for AJAX advance search (multiple params)

Hello,

Does someone know a Gem or a plugin that can help me building something
like
this advance search:
http://demo.neeraj.name/admin_data/advance_search/user?
I like it because it knows if it is an integer field or string field
and automatically fill the select field with the correct options
(greater
than, equal than, etc).

Or should I just try to implement my own solution, copying and pasting
somethings from admin_data?

Redmine has something similar:

In one hand, it fills the select field better then admin_data when there
is
a table relationship but on the other hand I can’t add 2 filters for the
same field. For example, I can’t search issues with “% done” greater
then 20
AND less then 70.

Thanks,

Fernando B.