1. Limburg prvince is served by Veolia-buses and some trains too. There are daytickets for either north or south of the province, and that for 5,50 is BUS only. You can pay a little more and also get the Veolia (ONLY!!!) trains-but only out off the peaks. They run to Valkenburg-Heerlen-Kerkrade.
2.there is also the EUREGIO dayticket-16 eur, but valid for 2 persons on sat/sun or ANY holiday in the 3 countries, that is valid :
-in NL the same as Veolia, incl. its trains-all day
-in DE on the whole of the AVV verbund
-in BE: in VLaanderen in Limburg province-they also have one, incl some NMBS trains-Liege-Hasselt. Thereis a fast bus Hasselt-to near NL-border below Eindhoven (Achel), from where you can connect into NL-by bus(-payable).
In Wallonie in Liege province, TEC buses and some trainlines-not ICE-HIspeed.
Cannot buy from NS, as its not valid on NS, but easy on any bus from driver.