This app was mentioned in 1 comment, with an average of 3.00 upvotes
Structural engineer here.. I'm still pretty traditional and use pen and paper for a lot of things. But I do use plenty of digital tools as well: Workflowy for all kinds of things like task lists, managing my projects, outlining for documents and reports etc. It's simple but very powerful (using #tags for things). Email of course. Inkscape for marking up PDF's and for plenty of personal work. AutoCAD for drafting, but that's just our standard. My phone's camera for so much site-related documentation.
Also, a colleague recommended the PlanGrid app for keeping photos, markups and on site viewing of drawings. But I found that my work is too varied to make this useful to me. But he swears by it for site reviews and walkthroughs.