This is the silver version of the Australian proof coin set for the year. It contains all the regular circulating denominations from $2 down to 5 cents. Instead of the definitive $1 of the "Mob of Roos" type though, it contains a commemorative one dollar coin marking the Centenary of the Armistice which signaled the end of World War I.
The Mint says about it:
The Armistice signed on 11 November 1918 brought an end to the fighting on the Western Front. For the first time in four and a half years, the guns along the Western Front fell silent on the eleventh hour of the eleventh day of the eleventh month. Since Ottoman Turkey and Austria-Hungary had also signed agreements by this time, the Armistice at Compiègne marked the end of hostilities during the First World War by recognising the defeat of Imperial Germany by the allied British, French, and American forces. Negotiations between the belligerents continued over the following six months at the Paris Peace Conference, culminating in the Treaty of Versailles. It was signed on 28 June 1919 - the anniversary of the assassination of Archduke Franz Ferdinand of Austria, which had ignited the global conflict five years earlier.
In 2018 the Royal Australian Mint commemorates the centenary of the Armistice with this evocative and moving year set that includes a specially designed $1 coin along with the standard circulating coin designs.