Free and Open Source Software

I recommend https://alternativeto.net/ since you just type in the software name and it will show alternatives rated by popularity. You can filter by many things including "open source".

At work we use Creo Parametric. I have a cracked copy of it at home, but I still prefer modeling in FreeCAD.

I think Microsoft tried creating something like it on Windows, so I guess it can technically count as a replacement; KDE Connect

I find LibreOffice to be way too heavy for light notes (My current light text editor is FeatherPad), but it's a great alternative to Word!

I use Claws Mail for my mail stuff. It works really well with my self-hosted email server and I really like the UI and such. On Windows I used to use the mail client that was pre-installed.

For text editing I've switched to vim and emacs (doom). I usually use vim for quick little edits to things that aren't worth opening up emacs and finding it in there and I use emacs for anything that'll take some time. On Windows I used VS Code.

For a web browser I use Firefox, hardened with arkenfox/userjs. Never had any problems with it and have been using it since before switching to Linux.

I do still use Calibre on Linux, but it's a good question. There doesn't seem to be a strong alternative for ebook management, and it does have good plugins for DRM removal, etc.

One of my favorite is fsearch, basically a one-to-one copy of Everything that is written in GTK

I am using Obsidian for quite a while now. I really enjoy the possibility to modify anything to my needs. What are your use-cases for Logseq (and Obsidian before)? And how are you liking the switch?

Kdenlive works, and is the best foss video editor imo, but I still haven't found anything as good as DaVinci Resolve (sadly not foss). DaVinci doesn't support common video codecs on Linux though (so you gotta get used to ffmpeg), and for basic video editing Kdenlive works fine, but for making cinematic things like short films or whatever there's sadly nothing nicer than DaVinci. I'd like to be proven wrong though.

Notepad->kate

I love Notepad++. I use notepad apps way more than I should, but I really prefer the lightweight, no formatting text editing experience. It's lightweight and can be installed as a portable version and supports all kinds of languages and plugins.

Edit: I suppose this isn't in the spirit of the question though since Notepad++ is not for Linux. Still it's an alternative to a Windows program that's FOSS. (2/3 on topic)