You should use single quotes ' or double quotes " around the URL in this case (and in general):

wget  'http://www.flareget.com/files/flareget/debs/amd64/flareget_2.3-24_amd64(stable)_deb.tar.gz'

From now, you should use this method in general when you use a string which contain parentheses as argument in a command. That is because parentheses are used for grouping by the shell such that they are not communicated in any way to a command. So, the bash shell will give you a syntax error:

$ echo some (parentheses)

bash: syntax error near unexpected token `('

$ echo 'some (parentheses)'

some (parentheses)