YES, you can!
You can leave a Grata for someone at another company the same way you would receive a Grata at your company. If the person you want to praise has a Grata account, then you would scan the person’s unique QR code and leave feedback.
Or, you can search in the Grata app for them through their employer's company Grata profile.
If the other person works for a company that is also a Grata client, then that company may have a web “widget” on their website (kind of like a chat button near the bottom of their page) that allows you to search for an employee and leave them a Grata from the web.