Nkoda is an app-library of scores, parts and sheet music on subscription. Not only is it a sheet music reader, armed to the teeth with all the tools you'll ever need, but it also contains the full catalogues of the top 100 music publishers. Users can annotate, layer, share and save these works offline to ease their practice, study and/or performance. Not only that, but the app can personalize every individual Nkoda account, through the settings that you input, by recommending pieces to you that suit your instrument, style of play and ability.
Like STOMP, Nkoda is available across iOS, Android and Windows, on seven different devices.
Cost: Free (Offers in-app purchases)