If when trying to open Manuscripts you see the error message "Manuscripts.app is damaged and can't be opened. You should move it to the Trash", it means that the copy you downloaded was damaged during download and the app has detected that when it was launched (or strictly speaking it is the operating system that has detected that).
The integrity of the app is checked on launching the app for the first time to ensure that it has not been tampered with and indeed that it has not been damaged. You can fix this issue by…
Downloading the app again using your regular web browser, from the Manuscriptsapp.com website (direct link: http://updates.manuscriptsapp.com/apps/manuscripts/production/download).
If you continue to hit the same issue, that can mean that the bad copy of the downloaded app has been proxied somewhere on your ISP, or more generally that a HTTP proxy somewhere between your ISP and your computer has the bad copy. You can work around this with the following steps:
A. Open a terminal window (by opening /Applications/Utilities/Terminal.app)
B. Type in the following and hit Enter:
curl --noproxy rink.hockeyapp.net,updates.manuscriptsapp.com -L \ http://updates.manuscriptsapp.com/apps/manuscripts/production/download > Manuscripts.zip
C. Decompress Manuscripts.zip by double-clicking it in Finder.
E. Replace the copy of Manuscripts.app at /Applications or ~/Applications with the copy you have just downloaded.
F. Open up the resulting Manuscripts.app
If you continue to hit download issues having followed the steps, please contact firstname.lastname@example.org for further assistance.