Allocation form module, which is is designed to allow instructors of a course to create slots that the students can sign themselves, is anew plugin in the Moodle plugins database which is released in this week only.
The Allocation form can be used to provide more than one choice (“choose three workshops from the following selection”) and/or to have students allocated to their choices fairly based on the overall choices/preferences made by all students using the Allocation Form.
You can download the Allocation form plugin from this link: https://moodle.org/plugins/view/mod_allocationform The plugin is supported for Moodle 2.7+ versions. The plugin is maintained by The University of Nottingham and Barry Oosthuizen.
There is a nice wiki guide on how to use the Allocation form plugin in your Moodle course here: https://bitbucket.org/uonmoodle/moodle-mod_allocationform/wiki/Home