I created a website for renting games online in my country.
Spended endless hours on working on it.
It was my first major project so a lot was learned.
I wrote my css and on some revision changed to bootstrap which helped out a lot.<p>What i learned, is to get a good partner.
We were two cs friends and decided to do this.
I Designed, developed, re-developed, promoted, promoted some more, took games to customers etc.
He ... well did nothing ... he expected it to work on its own.<p>Offcourse after a while i gave up my self but it did fail.
Lesson learned. Dont force your self to get a partner, unless the partner is worth it !
I had more than 1 ideas for which I registered domain, and then planned about it in spare time.
What I learned is plans don't always work. if you have an idea, its better to decide if its worth it for you to spend time on it. If the answer is yes, then instead of too much planning, its better to immediately get started from day 1. Even spending 30 minutes each day on building on that idea is lot better than just planning it.
All of my programming languages. I learned pretty much everything I know. I learned about memory management, processor architectures, all that fun stuff. Unfortunately I never got to that point where my languages were incredibly popular (or even usable for that matter...) and I could write a blank check for myself as the creator of a famous programming language ;)