Xero is another accounting application that competes with the likes of Quicken and MYOB. It isn't the first application-as-a-service in this market, but it is, IMO the best.
I hate accounting, numbers and tracking invoices and bills. But I don't like paying accountants to do it for me either. However the folk at Xero got everything right in automating an otherwise boring task that you normally pay $1000 of dollar for an accountant to do. I spend about 20 minutes per week telling Xero what account / category each of the transactions falls into -- and that's all I do!
I repeat; That's all I do. Xero takes care of the rest. I don't even need to import my bank statements - Xero does that for me too. Look how easy doing my GST returns was;
It took me about 1 minute to locate the link that took me to this (obviously I've blacked out the actual numbers);
The lengthy part was completing the form on IRD's website, which is just a matter of copying the numbers.
Of course none of the GST stuff is very useful if you're business isn't registered in NZ, but the other features are fairly generic and apparently they're already moving into the UK market with this.
The only thing Xero hasn't got right is the platform. They wrote this from scratch on the .Net framework, and it shows in the many small but annoying bugs. I've submitted several bug reports to them and they have been very communicative, responsive and most were fixed promptly. But they shouldn't need to waste resources on issues like broken login forms, broken forum notification services, basic search requirements etc.
I guess some folk still haven't realized that these sorts of issues have already been dealt with and that there is no need to reinvent the wheel. That's what frameworks like drupal are for! :)
Actually drupal + contrib modules could probably do 60 to 75% of this complex web app out of the box. The other 40% would be easily done with a custom module through drupal's hooks.
An open source alternative to Xero is SMB Ledger.
Update
The quality of my experience with Xero was great when I wrote this 2+ years ago and has improved since then. They now have the features I was missing at that time as well as other additional features — some of which I use. The support team is still very responsive.
I still regret that I am doing my accounting with proprietary software. And I think it's a little pricey for my use (contractor with low number of foreign-currency transactions) — but still excellent value. They have packages now which allow you to get less feature-packed versions for a lower fee.