What is the legality of gifting software titles/licenses I'm no longer using?

Many licenses are not transferable pursuant to the license agreement that came with the software, so it does not matter if they are gifted or sold. Thus, what you can do is only legal if the licenses permit you to transfer them.

Each license would need to be examined to see if what your propose would be a breach. Statutory First Sale Doctrine might protect against copyright infringement if any of the software may have registered copyrights and federal common law exhaustion of rights (similar to first sale doctrine) might protect against patent infringement if any of the software may be have enforceable patents.