In Australia, Solo (pronounced Soul-low), is a lemon-flavoured soft drink manufactured by Cadbury Schweppes.
Solo was launched in Australia in 1973 as the ready to drink version of traditional 'pub squash'. It is positioned as a very masculine drink and has had many television commercials that play to it's overtly male image, the latest being "Man Cans" which has been highly successful in Australia. There are 3 variants of Solo: Regular Lemon, Lemon & Lime and Solo Sub (no sugar). It is the market leader of lemon soft drinks in Australia and grew by over 30% in 2007.
Solo was launched before Rondo, so Rondo was an imitation brand launched in the US. It no longer exists.
It would appear, from can design and slogans, that Solo is the Australian version of the American drink Rondo, which was available during the late 1970's and 80's.