There are a ton of cool projects online, and especially on GitHub. I know there a ton of other places, but I mostly use GitHub, so I decided to go through my stars and share the most interesting repos.
OpenTTD
OpenTTD is a simulation game originally based on Transport Tycoon deluxe. It's genuinely a good game with solid game mechanics and charming pixel art.
3x3 Generator
This one is for the anime fans, That want to show off 9 anime in a 3x3 format. Comparable to a topster for music. This has been helpful to me in the past, since making a 3x3 is rarely worth opening an image editing program. I also like the multiple download options, and the fact that it is not dependent on one single image source.
Chess-Coding-Adventure
This project has motivated me to keep writing interesting projects (and more importantly, to write projects that I enjoy). Sebastian Lague's videos are incredible, and provide a lot of insight to the programming niches he explores. You can watch these videos here. I especially recommend his two chess bot videos and his fluid simulations.
PCSX2
PCSX2 is a great ps2 emulator which has been in development for 20 years. 99% percent of all playstation 2 games ever released are at least playable on the software. It's a great project that I use myself a lot of the time. And it's a testament to PCSX2's quality that people keep using it.
Notepad++
Notepad++ is a great lightweight text editor, that I also use a lot. I'm probably going to switch to it full time after my Webstorm/Intellij/whatever student license runs out. The project has been continuously developed for 21 full years and counting. There are also countless plugins that have been developed for its ecosystem.
My favourite features are the great binary and hex editor, the hashing functions and the export to html feature.
animdl
This is a cli-app to stream and download anime. I use it daily. The only downside is the fact that you have to download a media player and configure the program to use it, which complicates things slightly. Other than that, nothing but praise for this project.
and that's that. I have enough other projects that I could probably make this into a series. If I do, I probably won't write another installment for a while. I hope you checked some of these projects out, because they really deserve it.