I am highly experienced with Lotus Notes, as I am working with it for 7 years and have developped several very big database applications for user groups up to 10 people. Approach can be used by several persons at the same time, from very easy up to very complex calculations can be (easily) handled with approach, an enourmous number of dates can be put into one database, it can be used simultaneously by several persons etc.etc. We are using approach as a project tracking system, for various charging- and billing procedures plus for aa big number of reporting features.
It is true, that approach is not supported any more in future, but be sure, there will be always enough persons, who can handle it. Moreover, you are true, there is no documentation available, in the last 7 years at least, I did not find any except some very very basics for the first 10 minutes while creating a database! But, the help function is not too bad! What I have learned is all from experience and I must say again, approach is a brilliant program for a lot of applications.
What you are looking for, could be handled extremely well with approach (I guess, from your mails....).
We support all SmartSuite Programs on www.xpertss.com. We started the site in 1999 so it is a storehouse of informarion.
My specialty is Approach and I host that area on the site. I also do custom development in Approach.