Uvlechtichah baderech is a free app with tons of sforim
Powersefer costs but I got it a year ago and use it all the time. It has hundreds of sforim to download and they keep adding more. Now they are working on keeping up with the Daff yomi by adding misechtos with the tzuras hadaff. It has searches, bookmarking, highlighting and you can write notes at the side of the page