I'm Korean so let me explain about the company.
Daum KaKao is combined company of Daum communications & KaKao.
Daum Communications is an internet company, mainly focused on internet portal service like Yahoo!. (It is second largest portal in Korea, the first is Naver)
KaKao made a KaKaoTalk, which is dominant messaging app in South Korea.
Naver, which is the number one internet company in Korea has both of internet portal and messaging app (LINE, which is dominant messaging app in Japan and Taiwan) so Daum and KaKao are merged in 2014.
Daum KaKao now focusing on mobile service since it has dominant messaging app in Korea. The reason why they acquired Path is they want to enter Southeast Asia market, which Naver and Tencent WeChat already have largest portion. (Daum KaKao said that they acquired Path because of Indonesian market. Path has many users in Indonesia)
Yes, LINE already has many users in Spain and other Southeast Asia countries.
KakaoTalk is launched at 2010, before the smartphone market is matured. At the first time KaKaoTalk was made, Samsung and LG (both of them are Korean tech giant) dramatically produce many Android device, but there's no wonderful messaging app. (WhatsApp is not an free model, and other messaging app's quality it not that good) After KaKaotalk have gained lots of popularity, Naver made two messaging app named NaverTalk and LINE. NaverTalk based on Korean market and they failed since KakaoTalk already occupy all the smartphone. But LINE is based on Japan and they succeed, so Naver threw out NaverTalk and focused on LINE.
At this time, Daum (before merged with KaKao) made messaging app named MyPeople. They have many users in Korea, but didn't make a profit because of KaKaoTalk. And MyPeople also removed from the market after Daum merged with Kakao.
I've heard of KakaoTalk before; it's one of the most popular messaging applications in South Korea. According to Wikipedia it's used by 93% of smartphone owners in South Korea [1]. Daum Kakao is the parent company, and looks to have their fingers in a lot of generic web services pies.
In turn, KakaoTalk is extremely similar to LINE, an application developed by the Japanese subsidiary of Daum's rival Naver. LINE seems to dominate the Japanese messenging market almost as strongly as KKT dominates South Korea (it's probably not possible to be functional socially without a KKT account there).
I've lived in Korea, my experience was you gave out phone numbers when meeting new people, KakaoTalk automatically scans new contacts and adds them to your KakaoTalk contacts and all subsequent texting and photo sharing was through KakaoTalk.
I only texted one person regularly while I lived there, my boss; my boss had a KakaoTalk account but didn't use it (with me at least).
I still use it, it's a very good messaging application with some pretty well implemented features (and excellent custom emojis!).
KakaoTalk is very well realized and really fun to use; the privacy side leaves me queasy, though. KakaoTalk conversations are known to be under government surveillance, and the KCSC is a troublesome institution in general (cf. http://opennetkorea.org/en/wp/administrative-censorship).
Currently living in Japan, and I haven't given my phone number out to anyone yet. It's all exchanging LINE info (mostly using the QR functionality, sometimes just the ID). Almost everyone has a Facebook, but I don't think the messaging component is widely used. Almost all messaging, and even most voice calls, go through LINE.
Which I always thought was strange, given LINE generally provided a better experience and Naver is stronger in South Korea than Daum, at least in the search provider/maps areas.
Well, KakaoTalk was first -- they launched in 2010, and NHN launched LINE to the Japanese public in mid-2011. I'm actually not sure when or in what capacity Naver tried to port it to the Korean market. It would have needed localization beyond just UI translation. I've only used LINE for business, but I imagine the stickers (large emoji) that are a big part of the user experience of both apps when used casually were initially tuned for Japanese emoji culture (which has a fairly rich, complex history, that is intertwined with various popular Japanese characters and memes). So I'm guessing there was a significant time gap.
Saying KakaoTalk is the most popular app in SK is a huge understatement. It's like mode of communication there, seeing the number of hours people spend on their phones.
