Minetest - foss alternative to Minecraft with massive mod community.
Jellyfin - Github repo FOSS Media Server. Free clients available for most major platforms: Apple TV, Roku, Kodi, etc. Think of it as roll-your-own Netflix with optional support for Music and Pictures.
whoogle search - self-hosted search engine “proxy” removing Google tracking and spam…
Keycloak - self-hosted SSO solution supporting SAML and OpenID Connect
Openmediavault - Network attached storage (NAS) solution based on Debian Linux
Portainer CE - Portainer Community Edition is a lightweight service delivery platform for containerized applications that can be used to manage Docker, Swarm, Kubernetes and ACI environments
Backuppc - An ideal system for backing up computers, a lot af ways to connect (nfs, ssh, rsync, samba, etc…). Uses deduplication and flexible son-father-grandfather architecture. Runs in our barn and uses power line communication to leech all computers that I have running in the house (NAS’s , PC’s) and in the data center (Ubuntu server 22.04LTS).
Jellyfin - Github repo FOSS Media Server. Free clients available for most major platforms: Apple TV , Roku, Kodi, etc. Think of it as roll-your-own Netflix with optional support for Music and Pictures.
I’m really not a fan of Jellyfin, it always felt like an “also-ran” that was late to the party and didn’t scratch any itch that wasn’t already addressed. I use Kodi instead, it’s a lot more flexible and has a lot more extensions. (As a FOSS bonus, my media library is hosted on a FreeBSD server, served by Samba.)
Wordpress - Publishing and website building ( the world’s most popular website builder)
It’s also one of the world’s most insecure. You’re probably better off going with Joomla or Drupal.
I also like:
Keepass - Password manager that doesn’t keep your passwords on some foreign server. I just use my Nextcloud to make the database available on all my devices.
KiTTY - SSH client and fork of PuTTY. I like the fork since it has a couple more features PuTTY lacks.
LineageOS - Android fork that doesn’t have any google malware by default. I have it running on two phones and a tablet.
And since most people here are self-hosting…
Postfix/Dovecot/Roundcube - Self hosting mail. You don’t need to have all your mail sitting on some foreign advertiser’s servers, handle your own mail the same way you handle your own cloud services. The same Let’s Encrypt certificate you use for Nextcloud can be use for mail.
Jellyfin is a fork of Emby, from before they went closed source. I like it, especially the fact that it is open source, but unfortunately it does not run as well as Plex (at least on my devices). This is not so much because of the server part, but mostly because it lacks good clients on most platforms. However, as a Kodi user Jellycon might be an option for you.
For me, media streaming is pretty much the only software-thing in my household that isn’t powered by FOSS. I use Plex for local media, and of course also the well-known commercial streaming services like Netflix, Amazon, Spotify, Youtube etc, mostly on a nvidia Shield, which isn’t FOSS either.
On the desktop, however, I’m almost exclusively using Linux and FOSS software, so this would be a very long list… But I might post a list later on, that is limited to my self-hosted services…
There are many selfhosted stuff in my home server. Most of them are already mentioned in the first post. Few which I use but are not mentioned in first post are as follows,
It offers an excellent, easy to use Web GUI based reverse proxy (using nginx) for Reverse Proxy Management to get all those multiple selfhosted projects out to the internet. It also handles SSL for all those domains & sub-domains.
OpenWRT → For my router and WiFi Mesh Network (Fast Roaming)
But I don’t need it. As I said, Jellyfin is a solution looking for a problem. It solves nothing, and doesn’t actually offer me anything I need. It doesn’t even work as well as Plex for you, and you’re trying to defend it!
While I generally favour FOSS like you, I do rely on a few closed apps on Windows, such as Foobar2000 and Editpad Lite. But yeah, when it comes to self hosting, that’s a long list and I didn’t want to bog down the thread either.
I like the mention of why people like different tools. Very nice since one size will not fit all.
FreshRSS - migrated from ttrss after it discontinued hosting support. Vastly more flexible than nc news. Cannot use rss without filters and public sharing. Also, multi-user + integrations with other tools like…
Wallabag - keep offline copies from your bookmarks, rss, etc.
Need to update to get a lot of unnecessary features
Not allowing me to install it on laptop and desktop
Generally I donate some money to the community (Mozilla, Wikipedia, Freecad, others) once a year and click all of them away during the year (after adding them to a list).
Special comments are applicable for Nexcloud, LibreOffice and Freecad. It is amazing how much effort people put in these projects, to (as I see it) prove that creating a working program is not that hard as commercial suppliers try to let us believe.
Besides nextcloud, I am hosting with Docker a fair number of foss:
I’m using Mailu instead of Mailcow, it contains all tools related to a mail server including postfix, dovecot, roundcube, rspamd, clamav, webdav, dmarc, …
Wallabag for a Pocket replacement
Calibre-web for an online book library
Wordpress (2 different instances)
kopia for backup management
Navidrome for music server
Portainer
And all this running very well on a single raspberrypi 4 !
I’m also using Joplin and Keeweb (a replacement for KeePass) with the files stored on nextcloud
Piwigo photo management. I’ve chosen that because it can import IPTC metadata and write them back to the .jpeg including tags (with a plugin). This is still far away in Nextcloud Photo’s.
Please edit and add more! 
Open Source