ZThread is LGPL, you are limited to use the library in dynamic linkage if not working in a open source project.
The Threading Building Blocks (TBB) in the open source version, (there is a new commercial version, $299 , don't know the differences yet) is GNU General Public License version 2 with a so-called “Runtime Exception” (that is specific to the use only on creating free software.)
I've seen other Runtime Exceptions that attempt to approach LGPL but enabling commercial use and static linking this is not is now the case.
I'm only writing this because I took the chance to examine the libraries licenses and those should be also a consideration for selection based on the use one intends to give them.
Txs, Jihn for pointing out this update...
