Licensing
The licensing terms for NCSA Mosaic were generous for a proprietary software program. In general, non-commercial use was free for all versions (with certain limitations). Additionally, the X Window System/Unix version publicly provided source code (source code for the other versions was available after agreements were signed). Despite persistent rumors to the contrary, however, Mosaic was never released as open source software during its brief reign as a major browser; there were always constraints on permissible uses without payment.
Read more about this topic: Mosaic (web Browser)