There are two parts to this answer: 1. Microsoft SQL is a fully-functional database. To use it, you must to buy a license. 2. MSDE is a light version of Microsoft SQL.
MSDE substitutes MS SQL in most cases. DownloaderMDB includes MSDE license.
MSDE engine uses only one processor at the multiprocessors servers.
MSDE can be the only subscriber in the replication schedules.
In any other features, MSDE is the same matter as the MS SQL.
You’ll notice that MSDE substitutes MS SQL, even for middle corporative usage!
Also, MSDE license has been included in the following general licenses: MS SQL Microsoft Office Professional Edition DownloaderMDB
If you don’t have either MS SQL or Microsoft Office Professional, you can use DownloaderMDB Developer's MSDE license without any restriction for your internal use together with the DownloaderMDB. For additional information about MSDE usage, feel free to contact us at info@DownloaderMDB.com.