It doesn't need one, at least on Windows. If you install and use Steve's client, it works fine. It will be invoked by the browser when used with a SQRL login (at least one properly coded, such as on this site.)
Well, if you look at the banner on the top of these forums, you should find "SQRL Essentials" and one of the sub links of that is this: https://sqrl.grc.com/pages/getting_started_with_sqrl/ . It honestly has been some years since I set all this up and I forget more than I remember, but you should be able to just uninstall any browser extension, and then download Steve's client from the link on that page. It SHOULD install as a SQRL protocol helper for your browser(s) and when you click a "SQRL://" link it should ask you how to handle it, and allow you to choose the external SQRL.exe . From there, it should pop up the login page. The first time use is kinda cagey though cause you may not have a SQRL Identity yet, and that can kinda end you in a weird loop. In any case, create your identity, back it up (onto paper or some removable media, depending on your style) and then from then on, it should be possible to use it here on this site (double click your avatar icon on the top right and look for SQRL or connecting/associating... this link should work too: https://sqrl.grc.com/account/connected-accounts/ )
