The software is easy. Apt install debian apache2 php certbot and you're pretty much set to deploy content to /var/www. I'm sure any BSD variant is also fine, or lots of other software distributions that don't require a graphical environment

On an old laptop running Windows XP (yes, with GUI, breaking my own rule there) I've also run a lot of services, iirc on 256MB RAM. XP needed about 70 I think, or 52 if I killed stuff like Explorer and unnecessary services, and the remainder was sufficient to run a uTorrent server, XAMPP (Apache, MySQL, Perl and PHP) stack, Filezilla FTP server, OpenArena game server, LogMeIn for management, some network traffic monitoring tool, and probably more things I'm forgetting. This ran probably until like 2014 and I'm pretty sure the site has been on the HN homepage with a blog post about IPv6. The only thing that I wanted to run but couldn't was a Minecraft server that a friend had requested. You can do a heck of a lot with a hundred megabytes of free RAM but not run most Javaware :)