Any certified solution for navigation will not be on a tablet computer but be permanently installed in the aircraft.
And there are solutions for that which also display Nexrad data i believe.
Also just state the aircraft type and what you use it for and someone might actually have a solution for you. Not sure there are many answers that you could not find by using Google but oh well.
Try RNAV GPS drop in navigation system General Aviation as a start.
You could check out "Baron Pilot" on youtube.
Afaik he has some videos on his navigation equipment which i believe he can transfer waypoints into via tablet.