[drdaeman]

Possibly, LGPL or MPL?

You can link it with whatever proprietary code you want, but keep the LGPL library free. As long as you don't want to link LGPL-licensed library statically, it's quite simple to comply with license terms.

There's also MPL (v2), that's weaker than LGPL, roughly operates on file-level (rather than LGPL's library-level).

[gillianseed]

I've seen projects use LGPL with a added static linking exception (as in allowing it).

[mystikal]

I'm fine with static linking, it's even fine if you want to #include my source code. I never paid much attention to the MPL, will see, thanks.