One of my favourites was a forward-chaining rules inference engine written in T-SQL on MS SQL Server for a sixth-form college. The Management Information System (MIS) was called unit-e built by Capita PLC and probably cost a LOT of money.

It was quite a good system, the query builder for advanced users was excellent (every MIS should have one), but it had a fair amount of data duplication - names, addresses, previous address etc. And the admin staff had lots of name changes and spelling corrections to make. Also you had the data entry dudes who'd write a lazy name like fiesta try basharat instead of Fiesta Try Basharat.

So I built the rules-engine as a stored procedure (SPROC) called by triggers on tables. The rules themselves were just simple SPROCs and some not so simple but the rule interface was simple and so the system was robust. All of a sudden every letter sent by the school was formatted properly and went to the correct address! The admin team even gave me and my junior a present! And the 'junior' became an expert in SQL and learnt a secret ninja weapon (rules, inference engines and conflict resolution).

How many good things were created? How do you demo the transition of knowledge? How do you monetize the time saved? How do you portfolio the potential for benefit of new rules that haven't been thought of yet?

Expansion of knowledge, the beginnings of infinities, there's so much out there I love it!