FreeGameDev

When a user is online, you can call him(her) to play!
It's like this:
There will be a button called Quick invite in user screen.
When you click it, it will show a dialog of online users:

+------------------------+
| Ben |
| Sam |
| Pun Master |
+------------------------+

Then just click one(Click Ben), and you should choose your server then:

+------------------------+
| HK01 |
| Strasbourg custom |
+------------------------+

(Click HK01)After that, the other side will show a dialog:

+-----------------------------------------------+
| User Du has called u to play in HK01 |
| Play! Busy! |
+-----------------------------------------------+

If Ben clicked Play! ,then they(we) will goto HK01!
If Ben clicked Busy! ,then in Du's side will show:

+---------------------------------------------+
| Sorry, user Ben is busy |
+---------------------------------------------+

If Ben is installing addons, playing IN ONLINE SERVERS or dont respond in 20s, it will auto choose Busy!
Also u cant choose the same player in 30s(Avoid spamming)(The value can change in conf).
Also in server lobby u can also use the feature but it wont show server selection dialog.

This is a cool idea . But people may not want to be disturbed even when playing a local game. For example, when people are playing against a ghost and trying to improve the time or beat a WR, guess what he/she feels when this invitation dialog pop-up .

So the problem is that most of the time when people opens STK, they will either be playing local/online race or installing add-ons. There may be little chance that this invitation dialog is allowed to show up . Here are some ideas:
1. Make the dialog in a location that minimizes the distraction of a player when he/she is playing a local game. Maybe placed at the bottom or top of the screen with just one (transparent) line, and does not have any effect (on the key press) if the player just ignores it, and the dialog will disappear after 20s.
2. Set a 'Busy' status. If a player does not want to be disturbed, he/she can set his/her status to Busy, instead of Online. In this case, the dialog will not show up. So a player will have three status: Offline, Busy, Online.

Thought more about it: just 'Offline' can also solve this problem. People can choose 'offline' if they do not want to be disturbed. In this case, no need to implement the 'Busy' feature.

While in game I think to use a message like the "Name(s) is/are online."

One that says "Name(s) want(s) to play with you on Server."

When you exit the race then you will get a popup saying join/close.