I like this one. (though it would be better without the "web 2.0 shadow" :p )
I did post a version without the shadow Wouldn't it be better with a longer arrow and the power symbol nearer the SFML, like this :
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I certainly think it's worth trying!
Putting the logo on the other side of "SFML" might also be worth considering, since it could move closer to "SFML", because of the space the 'L' provides (in contrast to 'S').
The first several iterations had the symbol on the right, but after several suggest it be moved to the left I moved tot he left. I think the symbol on the left gives it a more natural left-to-right reading. But yes, fine tuning the kerning between the L and the symbol could be neat, but I think putting it on the left is best.
Here is another concept that someone sent me. The idea behind the logo is obvious, no need to explain
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It actually took me a long time to try and get the idea behind the logo (and there are a couple parts of it I'm still not 100% sure about). I like the idea (it's trying to visually describe what SFML does), but I think it comes across as busy/anti-simple.
I like Cornstalks' 3rd variant (shadow or not depends on context) - but wouldn't it be better to make the text colour brighter/more white? Right now it looks dark, dirty and evil.
I've posted several versions with the white text but no one ever said they preferred it (as opposed to the dark, which got mentioned several times) (at least I don't recall the white being preferred). But I feel the same, and actually prefer the white. I'll post some version with white text (and if there are things about the white text that could make it better, just say so!).
Alright, now I'm going to post some more variants/tweaks...