I often do work on weekends, and my venue of choice for this purpose is 64 Zerna. Unlike many other cafés, 64 Zerna is a large, open space, so even when it is crowded (which it rarely is), the room does not become noisy and distracting. 64 Zerna has a very cozy feel, with Parisian flair and a mix of couches and comfortable table seating. There are electrical outlets throughout, which means you can move around as you please with a laptop or phone and continue working or relaxing. Another plus for 64 Zerna is that it has a reliable Internet connection, which means no frustrating breaks in productivity.
64 Zerna is located along ul. Pravdy, a wide street with a large cobblestone pedestrian area. This is a nice part of downtown for a stroll or people-watching from inside, but it is often missed as there are no major tourist sites nearby. 64 Zerna serves the usual selections of coffee and tea and has a good set of desserts and snacks.
64 Zerna also has a small sound stage where concerts and movie screenings are held. I was once lucky enough to accidentally stumble upon a great concert here when I had only planned to stop in for a quick cup of coffee. Be careful, though, as these events often include a cover charge.