Upvote:0
In The Netherlands both the 9292 planner and the planner of NS (the main train company) allow for 1 extra stop:
9292:
NS:
For rail travel in Europe the Deutsche Bahn planner allows to choose 1 or 2 stopovers.
DB:
Upvote:5
I think Rome2rio offers what you are looking for, although I have no idea how optimal the choices are. For instance I tried a slightly random journey within Italy and Switzerland and the result sounded plausible enough (it involved trains, buses and ferries).
You add each leg separately, rather than say you wish to travel from A to B via C.