SteamIDFinder

SteamIDFinder is a tiny and portable application that retrieves player ID numbers of all users who have accessed their Steam account from your computer.
These unique player identifiers come in handy for banning or handing out administrative privileges, competitive leagues which require rosters to complete with Steam IDs, as well as for bragging rights (older accounts have Steam IDs with fewer digits).
Since installation is not a requirement, you can drop the executable file anywhere on the hard disk and click it to run. It is also possible to save it to a USB flash drive or similar storage unit, in order to run it on any machine seamlessly.
An important aspect to take into account is that the Windows registry does not receive new entries, and files are not left behind on the HDD after eliminating the utility.
The interface is represented by a small, regular window with a plain and simple layout, where SteamIDFinder automatically scans the Steam log files in your computer and shows all player ID numbers, along with their email accounts. You can copy these numerical values to the Clipboard by clicking a button. There are no other options available here.
SteamIDFinder is very low-demanding when it comes to CPU and RAM. It has a good response time and, although it has not been updated for a long time, it works smoothly on newer operating systems. No error dialogs were shown in our tests, and the app did not hang or crash. All in all, SteamIDFinder serves its purpose.