Borg backup, powerful backup software for self-hosted oriented users or enterprise automation.
proxmox, hypervisor that is performant and easy to setup for simple and complex virtualization needs.
bitwarden (combined with vaultwarden self-host), password management, secrets management, and available on basically all platforms and browsers. Self hosting your vault gives you peace of mind over who has your most sensitive data.
obsidian, a great notes app with polished cross platform applications that don’t do any funky proprietary storage shenanigans. Files are files and folders are folders.
kate (and most of the KDE suite), premiere Linux desktop environment suitable for customization and all the expected luxuries user would expect from windows or macOS. Kate specifically is a noticeable modern upgrade over notepad++ and rivals VSCode for programmers.
My only point was to explain that proxmox is great free software because it supports both simple virtualization needs, such as having several different VMs or containers running on one headless system with very little overhead, and complex multi-system setups that include multiple machines running proxmox and clustered together for both reliability and redundancy with distributed services and applications.