From the readme:<p>Parallel-hashmap or GTL?<p>The observant among us may have noticed that I have two github repos, parallel-hashmap and gtl, which both provide very similar functionality. Indeed the hash tables in both are equivalent and the code mostly the same. The main difference is that parallel-hashmap only requires a C++11 compiler, while gtl requires a C++20 compiler.<p>My recommendation would be to use gtl if you are compiling with C++20 or higher, and parallel-hashmap otherwise. While the included hash maps are equivalent, gtl is where new development occurs, and it will include useful new classes.