Lotus Software (called Lotus Development Corporation before its acquisition by IBM) is an American software company with its headquarters in Cambridge, Massachusetts. Lotus is most famous for its groundbreaking Lotus 1-2-3 spreadsheet application, which was the first killer app in the early days of the IBM PC and which helped spread the adoption of the PC. Thanks to Ray Ozzie's Iris Associates, it also developed one of the more powerful groupware systems, Lotus Notes. IBM purchased the company in 1995 for $3.5 billion, primarily to acquire Notes and to establish a presence in the increasingly important client-server computing segment, which was rapidly making host-based products like IBM's OfficeVision obsolete.