Substring search - could be realized with special dictionary. Needs special ranking function.
Exact search - search exact form of a word without stemming. It could be an option to all dictionaries to return an original word along with usual stems.
Phrase search
N-gram search - probably, special variant of a substring search
HTML parser
Configuration for a parser - join characters (blank, apostrophe, dot, underline, hyphen), option for splitting
translate(word, dic1, dic2) - translation dictionary, which returns word, normalized by dic1, and its translation (dic2).