"GNUstep - make your users smile today"
Great idea!
We should IMHO experiment a little with this phrase to try if we can
improve it (IMHO the "today" is not yet strongly enough saying that
GNUstep has a fast learning curve, rapid results and is mature - this
is why I had proposed to use the word "boost") - but it is already
exactly in the direction I am suggesting from marketing best
practices...
I should also mention one aspect of a good slogan: it is not comparing
to other solutions and some status quo - and it is "timeless", i.e.
does not emphasize on any current situation and is open for further
development of technologies. Your proposal is great in that aspect.
Another point is the word "smile" - this could also be mis-interpreted
as "sniggering". Maybe there is a better synonym (native speakers:
please!).