Régis Grison

This plugin is made mainly for french associations, because of the french 1901 law. Feel free to contact me if you think your contry have the same kind of need and I should make some adjustments for it. 
This plugin allow to handle association members by customizing the registration fields to avoid needing an additional listing. It also allows to keep track of the subscriptions. 
Note: This plugin will make use of the ACF (Advanced Custom Fields) plugin and will also contact my server to check for news about add-ons.

Law 1901 association

Handles members of an association and their subscriptions. Mainly for french associations under 1901 law.

shawfactor

Users of membership sites often have and use a membership number. Yet WordPress uses alpha numeric string for usernames for logging in. Why not use both by using the <a href="http://lhero.org/plugins/lh-membership-numbers/" rel="nofollow ugc">LH Membership Number plugin</a>.
LH Membership Numbers allows a user to login by typing in their membership number. Their membership number is the unique user ID that every user is assigned in the database. Optionally administrators can assign a prefix to the membership number (eg for my sports league <a href="https://princesparktouch.com/" rel="nofollow ugc">princesparktouch.com</a> it is PPT). That prefix can make the number far more unique (globally).

LH Membership Numbers

yesim the plugin author but this plugin works perfectly as described (it is a very simple plugin so it is not for everyone).

Don't be f-wit like bgtbbox (the last reviewer), read what it does and if you don't think it works a specified put something in the support forum and I'll look at it.

Works perfectly

Plugin to allow users to login by a number, their user ID (optionally prefixed)

Law 1901 association vs LH Membership Numbers