Examples of applications that use the Schnorr digital signature? I have made a study on digital signatures, especially on the Schnorr digital signature, and I was just wondering if there is some way I can find names of actual (known) applications that have applied and used this kind of digital signature. 

I haven't been able to find anything by myself, so any help is appreciated.
Despite their theoretical security advantages, Schnorr signatures aren't very popular. Probably because they were patented. Since the patents expired in 2008 they might rise a bit in popularity. But probably only in the elliptic curve form, and not in finite fields.
I don't know of any application actually using Schnorr signatures, but I know several that plan to or at least considered it. Either in the form of EC-Schnorr or Ed25519.
Both of these are essentially Schnorr signatures, but on elliptic curves. Ed25519 adds a few modifications, such as making signing deterministic and a message hash that hashes R before the message, but it's still very similar to Schnorr.

Tahoe-LAFS plans to use Ed25519
Ticket #217 - Ed25519-based mutable files -- fast file creation, possibly smaller URLs
https://tahoe-lafs.org/pipermail/tahoe-dev/2012-March/007109.html
It looks like they'll include in some places in their next big release (1.10)

Cryptosphere plans to use Ed25519
https://github.com/tarcieri/cryptosphere#readme

Bitcoin developers considered using Ed25519:
Theoretical max speeds for ECDSA verification 
But it seems like they won't actually use it

EMVCo considers using EC-Schnorr in their EMV standard

EMV is a global standard for credit and debit payment cards based on chip card technology. As of end-
2010, there were more than 1.24 billion EMV compliant chip-based payment cards in use worldwide.

From the EMVCo homepage

What is the EMVCo position on elliptic curves or other alternative cryptography?
EMVCo constantly reviews alternative types of cryptography. For further information regarding elliptic curve cryptography with EMV see the ECC draft of Book 2 (June 2007) located on the EMV website under Specifications &gt; Additional Files &gt; New Cryptography Drafts. The EMVCo Security Working Group is considering the use of ECDSA (or Schnorr ECDSA) for offline card authentication and the use of ECIES for offline PIN encipherment.

From EMVCo Security FAQ