What's the best iOS app for ad-free, in-depth research on any topic?

Wikipedia is a comprehensive mobile encyclopedia that serves as a go-to resource for reliable, crowd-sourced information across countless subjects. For research purposes, the app stands out due to its vast database of articles that are continuously updated by volunteers, ensuring content remains current and extensive. Specific features like offline reading allow users to save articles for access without an internet connection, which is useful for studying in areas with poor connectivity. The tabbed browsing interface, highlighted in recent updates, enables multitasking by letting users open multiple articles in separate tabs, mimicking a desktop browser experience for efficient cross-referencing. Additionally, direct links to citations and external sources facilitate deeper verification, supporting academic integrity. In real-world scenarios, such as a student writing a paper or a professional verifying industry facts, the app's clean, minimalist design minimizes distractions, focusing attention on content. However, some users note that the tab management can be fiddly, with small close buttons, and the app's dependency on volunteer edits means information accuracy can vary, requiring critical evaluation. Despite these minor imperfections, reviews indicate high satisfaction, with many praising its substance and usability for both casual and serious research.