Okay - from the begining I think.
What you are suggesting, basically already exists. The software is called Thyme (US$50 for a site license)
Now: To break down your idea.
- Calendar accessible via web OR iCal format (which means that while you can add/edit/delete events via the website, you could also do the same from an iCal program such as Mozilla Sunbird, or iCal. I think this would make it easier to work with and update.)
This synchronisation is through either a protocol called calDAV or one called webDAV - it has to be installed on the web server. Not many places actually support webDAV (and that is a real shame IMO)
http://midphase.com/ are one of the few (you have to ask them to install it).
- File storage space for contact lists, images, documents, etc.
Something you would expect anyway really - using webDAV for this as well would be damn handy (easy integration into the operating system)
- Notifications via email, SMS txt msg, etc. for different things (new event posted, rehearsal cancelled, etc)
Again, really nothing special - I can do that in most calendar applications, however it is a feature I do not use - I like to write the emails myself, it reduces the number of 'I did not get the memo' messages if you do it yourself. Then again, some people may like that sort of thing.
- Enhanced login system (username/password combo could be used as "showname" then a password of your choosing, OR you could have each member of your cast have their own user name, each with their own access permissions/groups, that shows only specific information related to them [ie/ cast only sees cast rehearsals, while tech sees all rehearsals. Or you could allow the technical director to post updated cue sheets for the light/sound techs])
Two stage authentication. Showname/Password to view the site, then the ability to log in as a 'moderator'/'editor'/'admin', using user/group type arrangement
- Message board (like this one) that allows everyone to talk about anything.
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Also, would you pay for something like this? I was thinking of making this a subscription-based service of maybe $10/month or something, just the cost of keeping the servers online. And, having worked for a software company before, I know the importance of updates/fixes to the software; so if someone says "hey is it possible to add x?" I'd do my best to add it.) So $10/month for a web-based calendar system that can also be accessed from software like Outlook, Sunbird, iCal, etc. with web space for file storage, notifications, message board, etc. that would constantly be updated with new features that YOU request. Would it be worth it?
Personally, no. I would not pay $10/mo for that sort of service.
Now I do not want to put a dampener on your idea - it has merits, but the technology is largely pre-existing, in fact I already run something similar for most of my shows (I will post something for folks here to play with later on when I have the time and am close to my server) - about the only thing lacking is I do not have web based editing of the calendar, and I write my own emails - however changing the email situation would not take much effort on my behalf.
I know most people out there are not computer guru's and would find setting up a server slightly intimidating, fair enough too, but I also think that it is not the individuals who would be purchasing such a solution - it would be the companies.
And from my experiance, a company which is willing to invest in such a service is the type which already has some form of IT infrastructure (be it just a simple website or other) and therefore would be after something that runs on their server, not hosted on another and that they would have complete control over.
Now IF you aim for the smaller companies, the average show length (including rehearsals) is between 3 and 5 months (your pricing scheme, US$30-50), for a show like that, it would not really be worth the trouble for them. And it would also mean you would have no guarantee of income.
AND... The host I pointed you at (midPhase) gives you enough 'stuff' to be able to host 120 shows, giving each about 100mb web space (more than enough, hell you could probably get away with 10mb each (1200 shows)) for US$7.95 and will pay for your domain... $10/mon would be making substancial profit even with only 2 or 3 customers.
I wanted to say some other stuff, but it is 1:30 in the morning here and I think I have gone off my tree slightly, so I will leave it at that for the moment.