HandleHud is another interesting project for GNU / Linux that you should know. It is completely free and open source, so you can view the source code or download it from their site at GitHub. And now it's news because it has been updated, with some important contributions from its developers.
MongoHub comes to fill a gap of tools that existed in the GNU / Linux operating systems and that surely players will appreciate. In this case, it allows monitoring of some data, benchmarking, etc. A handy HUD that works with all games that use OpenGL and Vulkan graphics APIs.
In fact, this latest version of MangoHud has added support for the powerful API Vulkan. In this way, it is possible to track the FPS at which a video game works, frame synchronization, read / write of the hard disk, benchmarks, see the use of RAM and VRAM, limit FPS in a game, etc. With the latest MangoHud 0.3.5 version, you can now also display the currently playing Spotify song, choose a specific GPU for multi-graphics setups, etc.
Other new features that have been added to this powerful hub are support for XNVctrl for NVIDIA graphics cards, the ability to have a blacklist to prevent it from trying to run certain incompatible software (eg: some game launchers), and a good number of fixes related to the OpenGL graphical API. If you were waiting for something like that for Linux gaming, you don't have to wait any longer. MangoHub is the answer to your demand ...