Under Linux you can enable the compose key, with setxkbmap -option "compose:rwin"

This lets you prefix digraphs with rwin, and have them print unicode characters. This is (to some extent) configurable, although I am not sure on the location of the mapping.

EDIT: Some examples (default settings): ä ç ß ¢ £ ½ ⅓ ¼ ⅙ ⅛ » « ¥ õ ° — – º