Graphite is a really useful website for teachers to find high quality websites, games and apps, for tablets and computers.
It is completely run for and by teachers with experience in and out of the classroom. Every review is linked to curriculum areas and common core standards.
It is quite easy to search for a tool that has been recommended to you determine it's educational value but the real gold is finding something new.
Graphite is a non profit tool and as such completely free but more importantly just like us it does not receive paid reviews. Be sure to check out Graphite here.