The OPCODE library distributed as part of ODE is licensed under
the same terms as ODE (LGPLv2.1+ and BSD).

Quoting a public e-mail from the author:

    Re: TriMesh support and OPCODE added to ODE core
    Pierre Terdiman <p.terdiman <at> wanadoo.fr>
    2003-07-01 21:18:44 GMT

    > If he wants
    > to explicitly make it clear that OpCode is good under ODE's
    > license, that would be A-1 Super...

    "Opcode is good under ODE's license"

    I didn't put a license to prevent boring questions about licenses, but it
    seems it's not enough - I still get as many questions, regarding missing
    license.

    The only thing that would NOT be good would be renaming it "TopCode",
    changing the author's name, selling it at a very expensive price, and still
    managing to make money out of it :)

    ...I should add a license explicitely against this :)

    Pierre

Source:
    http://permalink.gmane.org/gmane.comp.lib.ode/3237