"According to its own statement, G Data has developed the company's first own virus scanning engine for five years. The technique is called Closegap and continues to rely on the concept of two scan engines. G Data's virus scanning engine, along with Bitdefender's scan engine, looks for malicious software.
Previously came the second scanning engine from Avast. For the time being, this will continue to be the case in G Data's corporate solutions, but in the long term, all products will be converted to close-gap technology.
Someone may come along and correct me if I am wrong but this is how I remember it.
GData used to be Kaspersky and Reliable Antivirus (RAV), I was involved with the business of bringing localized GData to the USA way back under the branding 'eXtendia Antivirus - AVK Professional'. Microsoft bought out RAV to use for Microsoft Security Essentials and GData transitioned to their own in-house engine as the secondary one around that time I believe. Eventually GData transitioned to what they are now.
Emsisoft, I believe that was A-Squared Anti-Malware or something. I forgot, but I used to use it when it was a stand alone. Emsisoft is basically A-Squared, Mamutu, Bit Defender in it's form today.