There is no real way to suggest new software at Beta Labs and there is a reason for this. The core Beta Labs team does not develop anything in practice. We are a very small team and merely a channel for the actual development teams to conduct beta trialling. We also do not accept ideas, since we do not have the capability to respond to them.
Please, do not suggest new software ideas on Beta Labs site. I know you would really really want to, but please, still, don't.
You can, however, give suggestions to how to improve the applications here (on their own forums). For example, you can suggest a new feature if you feel it is missing from a product and you believe the feature would make the beta better for its purpose.
However, if this feature is an "application wishlist for Beta Labs" or a "place to suggest new ideas in Beta Labs"... you get the picture :)
Now, if you STILL really, really want to suggest a new application, go ahead and comment this thread with your suggestion. But this thread only! I must warn you though, these ideas might not be commented or in any other way acted on by us at Beta Labs. Still, if it makes you feel better, go ahead. I like reading the new ideas myself, but I just hate that we can't really currently do much with them.
Edit: You can send suggestions for applications to this category, but the situation is still the same. We just don't operate in the mode that we could promise to allocate any development on the suggested applications. Sorry!