Python and Outlook-style rules

[Brian]

I'm about to create a system which will need to allow hundreds of
users to create and maintain their own rules in a similar fashion to
MS Outlook rules. ie.
Each rule consists of one or more user configurable conditions and if/
when the conditions are met then one or more user configurable actions
will be applied.

The conditions will be things like "a specified key in a dictionary is
in a specified list of values" (where the user can choose the key and
the values), or "a specific record is in the specified
database" (where the user chooses the primary key of the record and
the database table to look in).

The actions will be things like "send an email to address" (where the
user chooses the address and the email template to use).

The user will do their configuration in a browser. Also, I need to be
able to continue to add new conditions and actions to the system over
time.

Is there a python module (preferably free/open source) which already
does (some of) this? I can write the back-end logic easily enough
(although I'd rather not re-invent the wheel) but I'd particularly
like to find a widget or similar which will make the front-end look
nice and be cross-browser compatible.