As far as changed your life, there are not too many that i really love, that made a massive difference to how i do things. But there is one:
Paperless_ngx
ALL of my paper work, receipts, transcripts, tax, shares, council rates. Everything goes in there. We no longer have paper lieing everywhere (well, my wife is another matter, still keeps grocery shopping reciepts...). when i get soimething in the mail, i used the paperless app to "scan" it, upload it, then bin the paper.
An actual life change that i didn't know i needed.