https://github.com/telabotanica/moodle-block_selfenrol

This plugin uses enrol_self module. If enrol_self is enabled for a given course, this block will show user's enrolment status and suggest him/her to (un)enrol, and log in if needed.

This allows to hide the Administration block that is usually responsible for displaying an (un)enrolment link, and might not be wanted (confusing title, other options might appear, etc.)

Make sure to display it on "every page" so that it appears also on courses summary pages.

English and french versions included / versions anglaise et française incluses.