I am looking for an alternative spreadsheet to Excel, preferably but not necessarily open source, that allows a programmer to create a plugin that can update cells in the sheet from an external data source in real time. The spreadsheet would then internally compute all dependent calculation chains upon change of value.
This is similar functionality to what the RTD method does with Microsoft Excel. The rate of external data change could be moderate to high (whatever such relativistic terms mean).
Also the reverse process would be useful, i.e. detecting a change in cells and then sending that information to a plugin that can communicate with external processes.
Any recommendations or experience in trying this?
I am afraid you will not find any. The main consumers of the real-time spreadsheets (grids) are big banks and they usually invest in their own solutions. [Because they can afford and they used to see it as their advantage over the competition] Some of the solutions are very dated, but still going strong! Three years ago I worked on a system which was written in C++ (with TibcoRv as a backbone) and it was already five years old. It is still alive and kicking.
One of the strong points of the bespoke grid are “Excel-like formulae” where a user can use a field from the provided data dictionary. So rather than reference cells, you reference data from your systems. It makes formulae easier to implement and read. And of course you can export or share them; users really like that.