You can solve LP,NLP,Stochastic Programming, Network Programming problems.
Solutions are sent by e-mail.
Network programming page uses the well-known codes RELAX and NETFLO.
OPBDP & PLAM
OPBDP (Davis-Putnam Based Enumeration Algorithm
for Linear Pseudo-Boolean Optimization) is
a 0-1 integer programming code.
PLAM (Prolog and Modeling) is a modeling language.
Bertsekas' site contains some FORTRAN codes.
RELAX solves (nonlinear) minimum cost flow problem.
AUCTION solves the assignment problem.
There also exist some problem generators.
DIMACS Challenge 1 :
Softwares for minimum cost flow, maximum flow, matching problem.
NETGEN is a well-known problem generator.
NEOS Server
You can solve Network Programming problems by well-known codes RELAX and NETFLO.
Solutions are sent by e-mail.
Goldberg's site contains softwares for
min-cost flow, shortest path, max flow, assignment problem.
There are good test reports.