I'm glad to inform that new GLP solver has been connected to OO: pswarm.
Note that along with box-bound constraints
lb <= x <= ub
this one is capable of handling linear inequalities:
Ax <= b
However, I encountered some troubles in my KUBUNTU (such as "recompile with -fPIC" and then, after fixing it, "undefined symbol opt") and have connected pswarm within WinXP. I have mailed PSwarm author the issues but he hasn't responded yet.