Originally posted by Sublimity
Alright, cool. Thanks.
I'm just trying to come up with ideas for expansion of skill.
If networking is something you're interested in, you should try building a chat application, those are always fun, there's a small tutorial here:
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You could also try building a denial of service tool, not necessarily for use, but just for the experimental purposes, trying to implement a slowloris or SYN flood is cool.
If you're not so in to that side of things, check out the creation of games, building a video game is always fun, and C# has the oh so wonderful XNA framework.
Out of the ones you've mentioned in your post, Quiz Maker and YouTube Downloader sound the most interesting to me, things that I might actually use in my current life.
Oh! Another fun thing might be a password cracker, I saw you mentioned a password safe application, and if that interests you, you ought to learn more about cryptography. A fun idea would be to implement a program that can break the two "hello world" ciphers: Vigenere and Caesar, first have it determine which cipher is being used, then have it determine the key, perhaps a not extremely practical program, but great for people interested in the topic.
Another fun idea would be to learn about stenography, perhaps try to hide text in an image, that's always fun.