The City's Redevelopment Authority has unique powers of eminent domain and condemnation, as well as the ability to sell land at less-than-market-rate prices (including nominal fees) for redevelopment purposes.
Over the past few decades, the RDA has acquired and disposed of thousands of properties for everything from individual side lots (quite a popular program, in fact) to large-scale housing and commercial developments. Nonprofits have received land from the RDA, and so have commercial developers.
Many of the parcels the RDA has conveyed have been developed; some have not.
Currently, the Nutter administration is undertaking an overhaul of the RDA and its processes for dealing with vacant land in general. The mayor has appointed a task force, headed up by representatives of the Redevelopment Authority and the Managing Director's Office, who are trying to create a “front door” for the public to access vacant land, which is currently held and dealt with by about a dozen different city agencies.