of how quickly works should pass into the public domain has been a matter of scientific and public debates, as well as for software like video games. Public-domain-like licenses and waivers While real public domain makes software licenses unnecessary, as no owner/author is required to grant permission ("Permission culture"), there are licenses that grant public-domain-like rights. There is no universally agreed-upon license, but there are multiple licenses that aim to release source code into the public domain. In 2000 the WTFPL was released as a public-domain-like license/waiver/anti-copyright notice. In 2009 the Creative Commons released the CC0, which was created for compatibility with various law domains (e.g. civil law of continental Europe) where dedicating to public domain is problematic. This is achieved by a public domain waiver statement and a fallback all-permissive license, in case the waiver is not possible. The Unlicense, published around 2010, has a focus on an anti-copyright message. The Unlicense offers a public domain waiver text with a fallback public-domain-like license inspired by permissive licenses but without attribution clause. In 2015, GitHub reported that of the approximately 5.1 million licensed projects it hosted, almost 2% used the Unlicense. Another popular option is the Zero Clause BSD license, released in 2006 and aimed at software. As result, such licensed public-domain software has all the four freedoms but is not hampered by the complexities of attribution (restriction of permissive licensed software) or license compatibility (issue with copyleft licensed software). Public-domain software See also , Classical PD software (pre-1988) Public domain software in the early computer age was, for instance, shared as type-in programs in computer magazines and books like BASIC Computer Games. Explicit PD waiver statements or license files were at that time unusual. Publicly available software without a copyright notice was assumed to be, and shared as, public-domain software. Notable general PD software from that time include: ELIZA (1966) SPICE (1973) BLAS (1979) FFTPACK (1985) Video games are among the earliest examples of shared PD software, which are still notable today: Spacewar! (1962) Hamurabi (1969) Star Trek (text game) (1971) Hunt the Wumpus (1972) Maze War (1974) Colossal Cave Adventure (1976) Android Nim (1978) Rogue (video game) (1980) Ballerburg (1987) Many PD software authors kept the practices of public-domain release without having a waiver text, not knowing or caring for the changed copyright law, thus creating a legal problem. On the other hand, magazines started in the mid-1980s