SLiM is a login manager. It is currently the only one available for noop linux.
pkgr -i slim
To have slim start up on boot, you need to add it:
systemctl enable slim.service
You can edit the /etc/slim.conf file to set slim to default to a user and auto login among other things.
When you login using slim, it runs the ~/.xinitrc file, so for instance if you wanted to:
a) Start udevil's auto mount daemon
b) set your X keyboard map to dvorak
c) start MATE.
Your .xinitrc would look like this:
For multiple sessions, SLiM passes in the session name as the first parameter (you can change this in the slim.conf file) so you can start the correct one accordingly.