The original Halo, the full name of which is “Halo: Combat Evolved,” cannot be played online without downloading the actual game as of September 2014. However, fans of the series have made multiple browser-based flash games that are set in the Halo universe, such as “Flash Halo.”
The first game in the Halo series came out on the first home console released by Microsoft, the Xbox. Since then, games for the series have been ported to other platforms, including PC, Windows Phone and Xbox One.
The Halo franchise became so successful that at 2009 Comic-Con, Microsoft announced an animated Halo series called “Halo Legends.” The stories in “Halo Legends” were canon to the franchise.