One of the companies I previously worked for has a number of key projects that they have wanted to do for a long time, but never completed and still haven't started. I've got the technical and domain knowledge to do this, but not the time to contract for them full time (as I work full time in another position). Is it appropriate for me to develop this solution on my own time and then send them a trial version, along with an invoice if they would like to purchase it from me? I considered just approaching them about out of hours contracting but unfortunately don't think that's an option and think this alternative would allow me to develop this more flexibly and to the standard I prefer.
If I do go ahead with this - what would I have to consider (licensing, continual support, etc')?