This is a very simple and easy to use proposal tool. Looks like this tool is in the initial stage. However developer has put good thoughts in it and appears to be in right direction.

I would like to give following additional suggestion to the developer.
1. Please allow to add brand in the proposal. A company sells different brand products. So brand name and brand description field would be very helpful.

2. Please integrate smtp integration so that when client is selected and proposal is sent, the proposal goes both via email body and as email attachment.

3. Allowing payment in the same proposal is the most. Else if there can be payment link area where the customers can click and then make the payment via stripe link, that would be fine as well to begin with.

4. If developer allows multi company support via single login, it would help agencies.

5. This is a simple and straight forward proposal tool. Please allow chat code insertion so that when the the proposal is opened, client should be able to chat directly with the employee / company.

6. Javascript insertion should be allowed for various purpose.

7. Pabbly connect integration should be implemented as a lot of appsumo customers use pabbly connect.