Playnite Portable

Playnite is a versatile gaming library manager that allows you to organize your games (including ones that are not installed) from some of the most popular third-party platforms such as Steam, Origin, GOG, and Uplay.

Intuitive and interesting game library manager that also comes in portable form

Another highlight of this application is definitely the fact that it can be used just as well for DRM-free, locally-installed games. Before we dive into details, if everything from above sounds good, then there's possibly an even better option available - Playnite Portable.
As you can imagine, it does not require installation and, yes, you can take it with you on the go on a flash drive and enjoy your games on any foreign computer in a matter of seconds, if you do so wish.
There's yet another reason why you should consider this portable version. You can configure the app to automatically sync your database via cloud-based services such as Dropbox or Google Drive.
Other than that, please note that the app requires .NET Framework 4.6 or later on your computer's system, and, as expected, the presence of the official clients of the supported game management platforms (Steam, Origin, GOG, and Uplay).

No major disappointments regarding functionality and looks

Upon first launching the app, you are prompted to import the games from the aforementioned platforms and, as expected, you are also required to enter the official credentials of each one you plan on accessing.
Subsequently, you're bound to discover a black-themed and quite user-friendly interface of what is a very well-thought-out application. Once your games are loaded, the application should automatically provide you with all their associated details.
Of course, you can launch and install new games directly from the app's main window. You're also provided with a couple of options for organizing and filtering your games using multiple filters. For instance, you can create bespoke categories and your games by store.

Brings together all your games, both from your PC and from third-party platforms

Considering everything that has been said, it's quite obvious why Playnite might be appealing to some gamers out there. It provides a unified environment for managing extensive gaming libraries for some of the key platforms out there, and it does it brilliantly, without many compromises.
This version, in particular, should only make the experience even more appealing since it offers all the functionality of the installer application, but with the advantage of portability thrown in.