I am already aware of UML but I want to look at all the options before I pick. Essentially I will need to have a way (preferably visual) to plan out the flow and actions of programs. They will all be web applications written in PHP or Python.
What (preferably free) ways are there to plan a program in this way beyond UML and common flow charts?
Large white board, dry erase markers, time and collaborators always work in a pinch..and a digital camera is good to snapshot the progress(unless you have a really nice whiteboard that will save to a file).
This is a very simple workflow diagram system, and paper is about as free as you get.
The best thing you can do, is keep it simple, don't over engineer and favour an evolutionary design.
I would look into Mindjet's MindMapper program (www.mindjet.com) - it's basically a virtual white board that is very intuitive to interact with and can export to multiple file formats including MS Project, Visio, Word, PowerPoint (in case you have to pass the design along for "oohs and aahs" from the sales team). We've used it for initial design meetings and it is definitely a productivity booster.
There are templates for flowcharts, system design maps, etc...
It's not free (i believe around $300/license) but if it's a short term thing then you can take advantage of the 30 day trial offer at least.
I recommend you to start simple, UML actually tells you adapt their techniques to the size of your business, so don't over doit, but make sure to at least have a basic workflow diagram(a simple diagram is better than no diagram at all).
Basic circles and arrows should work, think in every circle as a page, and every arrow as a link. For more complex things like ajax, you can imagine that by doing click you go the "function page" and then return (two way arrow).
You can also have hidden processes like a login validation, a page that you really never see, but you visit and then automagically jumps to a welcome page(or the login page in case of errors).
I use Dia to make that simple diagrams(Just simple arrows and the usecase circles from the UML section).
I know I'm oldschool and this may not be helpful, but for creative planning I still like to take a few sheets of paper and a pen into a silent surrounding. No distractions from emails, colleagues, stackoverflow (this one is new), phone. No Visio. Just me, my ideas and a sheet of paper. Also great for code review.