I got it:
vela3:vibe.d sin$ cd examples/diet/
vela3:diet sin$ vibe
Notice: This VPM build script is deprecated. It is recommended to
use DUB instead.
See https://github.com/rejectedsoftware/dub
Checking dependencies in '/Users/sin/Projekte/vibe.d/examples/diet'
Compiling diet template 'diet.dt' (compat)...
Compiling diet template 'diet.dt' (compat)...
Listening for HTTP requests on :::8080
[0C879E01:00000000 WRN] Failed to listen on 0.0.0.0:8080
Running event loop...