Here’s my take, biased towards the ecosystem.
Libraries
- arrays and array programming:
vector
repa
hmatrix
- numerics
- random numbers
- parallel programming
- The
Par
monad
- The
- unicode and locales
text
andtext-icu
- parsing
attoparsec
tagsoup
- networking
snap
and/oryesod
- web stuff
- templating
- persistance
- databases beyond
hdbc
- no-sql storage bindings
- databases beyond
- graphics
cairo
sdl
opengl
- xml
haxml
- crypto
- processors and systems stuff
Techniques
- generics
uniplate
syb
- metaprogramming
- Template Haskell
- data structures
- designing data structures
- EDSLs
- designing EDSLs
- memoization
- designing with monads
Tools
ThreadScope
- Advanced FFI tools
c2hs
- using Haskell from C
- Tuning the runtime, esp. GC flags