In the early days of the Haiku project, a debate raged concerning one of the projects primary goals: maintaining binary compatibility with BeOS R5. The idea was that the only way an effort to rewrite BeOS would be successful was if folks could continue running the apps they already had.
Certainly, a lot of software available for BeOS is open source or actively maintained -- these apps could just be recompiled if necessary. Others -- PostMaster, Gobe's Productive suite and a few other crucial apps -- weren't likely to get rebuilt, either because the original author had stopped maintenance without being kind enough to release the source, or because it just wouldn't be commercially feasible.
