Graphical user interfaces (GUI)
Working with XML
Parsing mathematical expressions
Writing a basic type checker
An example web application, using the HAppS framework, is hpaste, the Haskell paste bin. Built around the core Haskell web framework, HAppS, with HaXmL for page generation, and binary/zlib for state serialisation.
The HTTP and Browser modules exist, and might be useful.
Graphical user interfaces (GUI) >> Databases >> Working with XML >> Parsing mathematical expressions >> Writing a basic type checker
Haskell Basics >> Elementary Haskell >> Intermediate Haskell >> Monads
Advanced Haskell >> Fun with Types >> Wider Theory >> Haskell Performance
Libraries Reference >> General Practices >> Specialised Tasks