I'm a long-time user of Trac. It's a Python based client-server application, which means you run it on the server, and the "clients" need nothing but a web browser to access it:
Example screenshot from one of my projects / Android clients (click images for larger variants)
It certainly matches your requirements:
Creation of tickets: Sure. That's its ...
A few years back, I've tried Redmine and it could be an option for you.
You can create tickets, they are called issues in this environment
Categorization of issues is possible
Priorities for issues can be set, too
Every issue can be discussed by adding comments
Issue tracking is integrated (for example by subscribing to an issue ...
Mantis Bug Tracker
I would suggest Mantis as few commenters already did. I'm using it successfully. It is:
open source – GPL
well-customizable just by configuration (workflows, statuses, categories, priorities)
mobile access addon (3rd-party, not free)
e-mail integration – creation of tickets from e-mails
Mantis is a great ...
WordPress has exactly what you're looking for. It supports multi-site and with a few plugins, you can have all the features you need. Here is a list,
WordPress with the multisite feature enabled
Multiple domains with the plugin, WordPress MU Domain Mapping
Drag and drop interface with the plugin, Page Builder by SiteOrigin
Above plugins and WordPress is ...
I have used the SiT! Support Incident Tracker (and actually compared it to other solutions).
It fulfils all of your listed requirements.
You can create tickets
Categorization is made with skills, products and sites
Priorities for issues can be chosen
You can add comments and see the history of the incident
Ticket tracking is possible
Rubedo is an open source multi-site CMS. It’s a perfect option for multiple websites:
You can share content between sites
In-line publishing capabilities
Supports multi language
I agree with Customizer's suggestion of Redmine. Our team has been using it for years and it's worked out great for us.
Just so you know, you can go to Digital Ocean and quickly spin up Redmine with their one-click install. Might be quicker than installing on your own server for testing.
To answer this part of your question:
Do popular CMSs like Joomla or Wordpress have significant advantages which I may lose using a CMS based on a framework?
Wordpress is very popular CMS, so it's very easy to find a support when you have a problem. You can propably find someone who know it in your acquaintances. Wordpress is regulary updated, and ...
LaTeX is a document preparation system. Strictly speaking, LaTeX is a markup language built on top of the TeX typesetting system; more generally “LaTeX” can mean a set of tools built around the typesetting system.
With LaTeX, you don't (usually) interact with a WYSIWYG editor. Instead, you type text with macro calls, like this:
Alfresco can do this, and it is Open Source.
Can handle huge amounts of data
EXIF data is automatically extracted and stored as metadata
Alfresco remembers who uploaded what when. If the uploaders are not the photographers themseleves, the photographer's name or id can be stored as metadata.
You can use tags and categories. Very useful for classifying. The ...
Maybe you'd want to have a look at Simitless. If I understand your question correctly, it should fit what you are looking for:
uses a declarative data model,
supports OAuth/SSO with Facebook, Google, LinkedIn, Microsoft, Slack, Twitter,
enables you to create your own database management web app - it gives you modules/fields (like spreadsheet columns) that ...
How about Emacs's Org mode?
Hierarchical/tree based structuring of notes — Check. This is its most characteristic feature, as a descendant of outline.el.
Multi user (simultaneous access to different notes) — This isn't provided by Org itself, but because Org documents are plain text, you can use generic tools such as SSH or version control systems (e.g., ...
Well, all these years later someone upvoted which reminded me of this question. There is one way to do it that I've found that works.
First, use RDPWrap to enable multiple RDP sessions if you have not already. Create as many Windows user accounts as you need.
Keep RDP graphical context alive while minimized 
Find the registry keys:
You search a database front-end.
I guess a Wiki software should solve your needs.
This way you can share and cross-reference your knowledge and the results of your investigations
Compared to a relational database this is very fuzzy, but creating a DB schema for your data types is hard work and would take too much time if you are new to databases.
KeePass does fine with multiple users:
http://keepass.info/help/base/multiuser.html - the 'Syncronize' option is what you want.
There's even an advanced option that automatically takes the 'syncronize' option when saving.
You just have to make sure that only people who need the database have access to the share and it should work fine (it does for me).
(I want it for university associations)
You will need to do a fair bit of customizing to get the functionality you want from the standard CMSs, I believe, although that would of course be possible.
However, I think Elgg would be able to give you most of the functionality you want. It is a "social networking engine", aimed in particular at "...
Take a look at GitLab. It fulfils all your requirements, it's open-source, and the platform that it's a basis of is a leading competitor to GitHub. You may either use that platform for free or self-host.
We are using Eventum for both customer support tickets and development issue tracking.
Creation of tickets - a click away
Ticket categorization - check
Ticket prioritization - check
Comments on tickets - set it initially, editable afterwards
Ticket tracking - check
Gratis - check
User > 50 - no problem
Server should run on ...