What I use for invoicing, organization & time-tracking
I was imagining a home-grown Latex based solution for invoicing - but what I actually went with is Debitoor (4€/month plan). They are a Berlin-based service for invoicing and bookkeeping. Which means my spreadsheet for tracking expenses could also be moved to the Trash. Using a service for which the country I live in is its home/core market - as opposed to some US-focussed company - was important to me. Hopefully less hassle when doing my taxes, and not getting sued because my invoices don’t contain some info required by law.
On top of that I use Trello Kanban boards for managing
TODOs & ideas (free plan).
And Toggl for tracking time spent on tasks (free plan). Their iOS app sucks on iPad though, you’re better off just using the website in Safari. For Chrome there’s also the Toggl Button extension that puts a button in the toolbar for easy start/stop/resume. Check out thefreelanceeffect.com for a nice review.