Kastner is a slick specialty café and community working space located in the outer part of Budapest's District 8. I like to come here for the spacious inside and to perch on the comfy mid-century chairs and watch the comings and goings of the park across the street through the massive windows.
The co-working area is upstairs and requires a ticket (€4-8 depending on the length of your stay). Lingering is welcome on the downstairs, too, but remember to order a drink periodically if you camp out. Breakfast pastries and sandwiches are also available.