Overleaf - The online platform for scientific writing. Overleaf is free: start writing now with one click. No sign-up required. Great on your iPad.
iMazing - iMazing lets you transfer music, files, messages, apps and more from any iPhone, iPad, or iPod to a computer, Mac or PC. Manage and backup your iOS device simply without iTunes. (was DiskAid)
TeXworks - The TeXworks project is an effort to build a simple TeX front-end program (working environment)...
Documents by Readdle - A central hub for all your files.
Fidus Writer - Fidus Writer is an online collaborative LaTeX editor especially made for academics who need to use...
FileApp - FileApp is an iPhone and iPad File System and Document Viewer.