Moshe, Basecamp is a great tool and I used it myself some time ago. However, for our purposes, it was simply not enough. I'm sure it is still great for some people. Clutterpad differs in many ways, but you will have to use it to really appreciate the differences. Here are a few:

1. Clutterpad is user-centric. That means you don't need to have different urls / accounts for different companies. Ths means that you can view all your todos / messages / etc for all of your projects for all companies from a single page. You can search through all your contacts, files, messages in all your projects from one page. There's no need to have multiple browser tabs open if you don't want to. Of course, you can also view stuff on a per-project basis too.

2. Clutterpad has a fully functional calendar with reminders and lots of other stuff.

3. Clutterpad does not have a flat file system. You can upload files, create folders, drag and drop files and folders, right click etc - so it's very simple and easy - similar to the file manager on your own PC.

4. Clutterpad has a contacts organizer. Every project requires contacts - suppliers, clients, other people. You can log all your communication with them here.

5. Clutterpad includes a private chat bar which you can use for your work - there's no need for separate IM clients. This is especially useful if you are somewhere where IM is blocked and you want to be able to talk about work with your colleagues, for example.

There are lots of other differences but these are the main ones.