Update again, mostly for @alberto and @nadia: Magic Spreadsheet v1 is ready to use.
Documentation and a few tweaks will follow tomorrow, but you can have a look already. All main mechanisms work. For now, there are two example projects based on our Budget Template spreadsheet, providing some bad (but fictitious) cashflow outlook.
The graph now only shows the company's total cashflow now, no longer the project-specific values. This is partially because project lines in the chart were just confusing, and partially for technical reasons. (You can always explore project cashflow by selecting parts of a project's column in sheet CashflowData2 and then looking into the footer to see the sum, representing the project's cash on hand value up to its last selected revenue item.)
Apart from that, I discovered that spreadsheets are a bad technology for everything except very simple, standard calculations and graphs. They're basically two-dimensional spaghetti code … or four-dimensional one, when also counting the "multiple sheets" and "multiple files" options. The budget template is ok, but at some point we might want to reimplement the Magic Spreadsheet functionality in Python. But that's 2-3 years into the future when @anu will be an advanced software developer who can handle this