How to manage startup applications in Debian 9?

There are (at least) two packages in Debian which provide tools to manage startup applications.

The first is gnome-tweak-tool; its “Startup Applications” tab allows you to manage your startup applications in your desktop environment.

The second is systemd-ui; it shows all the configured systemd units and jobs on your system, and allows you to start, stop, restart and reload units. It also displays the description and dependencies of each unit (but not the links to the documentation which may be given in the unit). It doesn’t seem to allow enabling and disabling units though, which is probably what you’re after.

You can use use Boot Up Manager, which is essentially a front-end to manage the scripts in /etc/init.d. It'll give you a view of what scripts are present on your computer and which ones are active. You can enable or disable them in the GUI. It does provide a level of additional information if you select Advanced and go to the Services tab. This includes priority, tags and a home page you can visit to get more detail. You can find more information on it here: http://www.marzocca.net/linux/bumdocs.html and install it with apt-get install bum

If you're just looking to add a program to startup, there was a (gnome-based) Startup Applications program with a simple click and add interface available in jessie (or in my installation at at least). I can't establish if it is present in stretch from a simple google.It may be worth checking to see if the option is available in your menu.

Startup-Watcher

Also as an alternative this application can watch for changes on 32 locations about auto-starting applications, services etc.

Captures