Overlaying objects
https://steamcommunity.com/sharedfiles/filedetails/?id=96752341
Glass bug
https://steamcommunity.com/sharedfiles/filedetails/?id=96752469
Light bug
https://steamcommunity.com/sharedfiles/filedetails/?id=96467894
Founded in 2004, Leakfree.org became one of the first online communities dedicated to Valve’s Source engine development. It is more famously known for the formation of Black Mesa: Source under the 'Leakfree Modification Team' handle in September 2004.