It's not exactly the newest castle on the real estate block, but Newcastle Investment is building quite an artillery. A real estate investment trust (REIT), the company underwrites and invests in real estate securities, real estate-related loans, and residential mortgages. Commercial mortgage-backed securities and similar instruments account for about half of the REIT's portfolio. Newcastle Investment is externally managed by Fortress Investment Group, which also owns a minority stake in the company. Newcastle chairman Wesley Edens is also a co-chairman of Fortress.