I've paid for RubyMine, and PHP Storm. Not exclusively Linux, but that was the platform I was running it on.

Not OP, but: I have sunk a few hundred bucks into Steam after it added Linux support. I had a Steam account before that, but I never purchased anything that cost money.

Intellij IDEA, also Steam or GOG games

As with others here, various JetBrains tools and Linux-compatible Steam games (I have 75 and counting). Also a file comparison tool called Beyond Compare.

If Adobe released their apps on Linux (more specifically Photoshop and Premiere) I'd buy them in a heartbeat. Unfortunately they seem more interested in supporting the iPad if recent news is to be believed.

Edit: Just remembered I have a Sublime Text license too, although I stopped using it a while ago.

A couple of months of Intellij because a customer wanted me to work on a Java project which used that IDE. I delivered in the first month and paid for the second one because I didn't realize it was autorenewing. That was a long time ago.

I also received a Steam game from a friend as Christmas present. I didn't pay but he did.

Probably nothing else.

I used to get my distributions from Walnut Creek, then bought a few boxed editions of Mandrake and SuSE, for several years subscribed to Linux Journal since the yearly days, occasionally bought Linux magazines with CDs on them, did FSF donations a couple of times, nowadays every time I download Ubuntu I always donate donations.

Likewise on Windows apps that I use regularly like Notepad++, jAlbum, Sublime Text, Paint.NET, Thunderbird, Firefox...

I'm also interested in this question. Because looking at myself, I have paid for several apps on both Windows and MacOS but never on Linux. Although to be fair I stopped using Linux as a desktop OS before I had the economic security needed to purchase apps in the first place.

I pay for elementary OS and Godot Engine on Patreon.

CLion and SmartGit

In current use:

- 010editor

- Jetbrains Toolbox

- VMWare Workstation

- Various steam purchases

Years ago:

- Corel Office

- Crossover Office