Ableton Live, Presonus Studio One and about a million VST plugins. Digital audio workstations and software instruments/effects are an area where open-source has made only limited inroads. Ardour was decent last time I used it, but since I got into Ableton Live with Push it's hard to go back to other things.
I want to jump to linux, but the prospect of starting from scratch on a new OS (or even a reinstall of windows) is just not feasible right now.
Adobe After Effects. Despite being an unstable spaghetti code nightmare, there is no other viable option for professional motion graphics designers.
Onenote! I use it for school and work, and love the syncing capability and the flexibility in structuring and organizing my notes. I also like the keyboard shortcuts and the way it can dock to a side of the screen to keep the main content visible
Would https://anytype.io/ be a replacement? It's very new so you might not have heard of it. It's designed like Notion, but it might have everything you need.
If your needs are more simple, https://notesnook.com/ could be worth looking into.
Other FOSS options are Joplin and Logseq. I'm an Obsidian user myself; not FOSS but the storage format is completely open which is the most important to me.
Sublime text. It is just so fucking good! Much more performant than even nvim.
firmware/drivers
Nvidia drivers. Back in 2019, I was looking to replace my Nvidia card with an AMD one, but decided I could put that off for a few months. Then COVID happened along with the cryptocurrency boom and prices skyrocketed to unreasonable levels. Nvidia drivers are honestly the last holdout on my machine barring perhaps some firmware somewhere.
Nationwide banking.
If it's free and open source and it's also software, it can be discussed here. Subcommunity of Technology.
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