I went to the tram museum in Gothenburg today, where among other things they had an exhibition on how passengers paid for journeys over the years. The information below comes from this display -- apologies for the quality of the pictures.
Before 1919 a system involving märken (a kind of stamp) was used, but in that year it was decided to use metal tokens instead. As I understand it, it was possible to pay the conductor (later the driver) with cash as well (up until sometime last decade, in fact). Passengers were, however, encouraged to use tokens as this meant that there were no problems with finding change for large-value banknotes or coins.
The first token was entirely devoid of text. On one side is a typical Gothenburg tram of the WW1 period and on the other is the city arms. These were introduced in May 1919 at an initial price of two for 25 öre. The price rose in December the same year to 15 öre each.
In 1922 a child fare token was introduced. This token was also more informative. One side carries the Göta Lejon, with the date (1921). Below the lion, BARNPOLLETT means child token. 'Inlöses efter styrelsebeslut', which appears on this and all the later tokens, means 'Redeemed according to management decision'. The child fare at this time was 10 öre. This token was designed by Karl M. Bengtsson of Gothenburg.
In 1924 the adult token was changed to one more similar to the child version, but dated 1924. VUXENPOLLETT means adult token.
The 1921/24 tokens remained in use until 1949, though their value changed. In 1941 fares rose to 20 öre for adults and 15 öre for children, but in 1945 the child fare was reduced to 10 öre again.
In 1949 the price rose to 25 öre and a new type of adult token was introduced, with a triangular hole. There is no mention of a corresponding child token. This token remained in use through three price rises, in 1951, 1952 and 1955, until 1956, when a paper coupon system was introduced.
I have yet to come across any of these tokens to add to my collection, though they do come up on Tradera from time to time.