Well its been out of fashion for a long time, but for some purposes a client side app is really the only answer !
Interestingly someone pointed out to me the Australian Tax Offices "eSAT" application (a multi-platform multi-lingual application for accountants) uses drools - and its a client side app !
This is an application that is distributed to about 12 000 accounting professionals (it has an offline and online component) related to superannuation (that's like 401k - retirement savings):
Interestingly, they use pre-compiled rules (being finance and government related, they tend to use a fair few rules !) - and only distribute the "runtime" as part of the app. One of the key constraints of this application is that it had to fit within a certain download size (so every dependency had to be analysed to see if it was really needed).
So there you go, client side apps are still around - and this one by Cordelta looks like a pretty good one when I tried it on my mac (they have distros for all platforms).
The ATO site where the app came from is here.