In the 1980s, before the Internet was available and when commercial online services were expensive, there were still other ways to obtain software besides just going to the store. One way was through disk subscription services. I'm not sure how popular these were on other computers but there were several for Commodore 8-bit computers. The most popular was probably Loadstar.
This particular ad is for one such disk subscription called Uptime. I'm not really familiar with this one and I suspect it didn't last particularly long. At least I don't recall seeing many ads for it. Searching the web, it appears that there were 21 issues of Uptime and that Loadstar actually bought them out at some point. Believe it or not, Loadstar continued to be published until 2007.
Read more: https://www.megalextoria.com/wordpress/index.php/2018/06/01/uptime-commodore-64/
OK, I consider myself pretty well-versed in computer history, and I'd never heard of Uptime before. This is amazing! Thanks for showcasing this one, @darth-azrael! :)
Assuming it was a monthly publication, it was around for less than two years. This ad is from the January 1988 issue of Commodore Magazine and it looks like the same ad had been running since September 1987. However, I don't see any ads for it after January 1988 so it appears to have only been advertised for about five months. I'm not sure if it appeared in other magazines or not...
My first computer was a TRS-80 Color Computer (CoCo). I was amused to see that you can still find emulators for these old computers and play the text-based adventure games like Madness and the Minotaur (Totally unsolvable).