Top 4 collapsable open source projects

Fast and versatile Adapter for RecyclerView which regroups several features into one library to considerably improve the user experience :-)

Android RecyclerView Adapter with nested items & expand/contract functionality

React native Accordion/Collapse component, very good to use in toggles & show/hide content

"TreeView - sub-cells simplified" (c). Enable subcells in UITableView with a single drop-in extension. CocoaPod: