OnShape for designing 3d objects. I’ve been using it for 3 or 4 years, after outgrowing TinkerCad (which is also good and beginner-friendly, but limited). It’s an online app, nothing to download or install. The free version is fast and full-featured. The only difference between it and the paid version is that in the free version your designs are all public. So if I were doing 3d design for business I probably would use software that resides on my computer. But as a hobbyist IDGAF.
Since you’re saying “pieces of software” and not specifically apps I will mention Node.js, the programming framework for javascript apps that run outside of a browser. You can develop websites and services or standalone apps that just run locally. There’s a whole universe of free packages people have created for it.