Microsoft seems to be trying exceptionally hard to bring Skype back to the way it used to be before the forced upgrade to version 8, and now yet another feature from the old days of the service is making a return. With the latest builds available for Insiders, starting with version 18.104.22.168, users can now enable notifications for whenever a contact comes online.
Unlike what used to happen in previous versions of Skype, these notifications aren't enabled by default, so you'll need to head into Settings -> Notifications and turn on the "Contact comes online notification" toggle. This kind of notification isn't very common among other messaging apps nowadays, so it's interesting that it's being brought back now.
This is just the latest of the many changes Microsoft has been making in order to win back some of the love Skype once had. Last week, the company announced screen sharing for mobile devices, a feature which has long been exclusive to desktop devices, even on competing services.
If the recent changes have interested you in getting back into Skype, you can download it for your platform of choice from the official website. If you want to get early access to new features, you'll need to download the preview version instead.