I hate post it notes for keeping track of things to do.. it's just not well suited to that task.
People use them as a way to keep a task always in full view so you don't forget to do it, but that's just using the available tools wrong.

Instead use a time manager app, I actually use the Samsung calendar on my phone these days, even though its just a task manager (not a good one) and calendar. I've come to know some shortcomings of using the Samsung app so I am looking for something else, although the app itself is visually quite pleasing.
I used to use a Franklin day-timer planner years and years ago, and I liked the way it had A/B/C priorities for tasks, then within those tasks , 1/2/3/4, etc.
So I could have several A1, A1, A2, B1, B2 tasks like this. Each day I have to manually forward incompleted tasks for that day to the next day then boost them in priority if needed. I have yet to find a task manager/day planner that is equivalent. Maybe I need to write one

None of the task managers I've tried have automatic forwarding of incomplete tasks to the next day.. they just leave them on the day they were entered and due and mark them RED(!) overdue something like that. Maybe that's the way most people want to work.. I'd like to see them just as a task list that's overdue and not hidden from me that I have to go look for them under some checkmark option or another page of the app.
As for time tracking on multiple different billable projects, there are also tools for that, although I have no experience with them .
Jira is nice and integrates with github and your code tracking well, but its not free.. for up to 10 people on your team, it's less than $10/month.
There is also the
free project tracking app called
Trello...from Fog Creek Software (the founders of the stackexchange sites, although stackexchange is now a wholly self-funded enterprise not owned by Fog Creek anymore).
Trello is indeed, way, way cool, easy to use and offers live collaboration, events, event subscriptions, alerts via email, web, chat and maybe even SMS(?? not sure). It really shines with teams, but there is nothing to stop you from using it as a single developer on your projects. There is also a small github to trello integration project (hosted on github) but it requires some additional thought on your part to maintain the integration (basically your commits to github have to reference a Trello card and it will be entered into Trello when you commit -- very basic, but it's a start )
All I, and I believe a lot of others, need; is sw that will allow me to make a note of what progress I made today, what needs to be done next time, and what did it cost, if anything
If that's all you really need then, as others have said, just have a file in your project stored in a repo like github.. call it STATUS.TXT and update it anytime you do some work and want to track it.
But tools like Trello (plus the github<->Trello integration) can allow you to update a status on a Trello page that your stakeholders can visit and view (stakeholders being anyone with a stake in your project getting completed on time )