Vim Spell Checking

Build-In Spell Checker

Activate for the current buffer (optionally set the language):

:setlocal spell
:setlocal spell spelllang=en_us

Source: Vim Spell-Checking (there is help how to automatically turn spellchecking on for selected file types)

Command Meaning
]s next marked word
`[s' previous marked word
z= show a list of proposed words
zg add marked word to the list of correct words
'zG` add marked word to a temporary list of correct words

see also: :help spell

Language Tool

Java program for spell-checking (not tested, yet)