I recently acquired a vintage clarinet that uses a fingering system known as Albert, or Simple, fingering. This is a system used by clarinets produced in the late 19th to mid-20th century. Some makers still use it. The more prevalent fingering system today is called the Boehm system.
Fingering charts for the Albert system are very difficult to find. Good news is this app has ALBERT AND BOEHM system fingerings. It is really indispensable to me, as I have clarinets that use one or the other system.
I’d rate the app a 5, were it not that to switch the fingering diagrams between systems requires you to select the fingering system you need, exit the app, and restart it. That’s a little inconvenient, yet tolerable as it is the only tablet or iPhone app to cover both systems.