Hello,
Outline was relicensed from GPL to LGPL about a year ago, so you can
use the library in closed-source / commercial applications, without
restrictions.
GLPL, as opposed to GPL, does not require you to license your
applications under any given license.
There's a good, human-readable article about the differences of GPL
and LGPL here:
http://fosswire.com/post/2007/4/the-differences-between-the-gpl-lgpl-and-the-bsd/
Regards,
Rasmus Schultz