AIML, Artificial Intelligence Markup Language developed by Richard Wallace, constitutes an open standard for creating your own chat bot.
For example, with the Bing Music bot, typing in "Hello" would bring up Adele's song (a link to her You Tube video, it looks like) rather than polite small talk.
A "Hi" in Bing News brought up articles with the word "Hi" in it. " it responded with different lunch hours instead of what was on the menu. You might ask around or try this thing called the internet." Cheeky.
E., brought to artificial life in 1995 by Richard Wallace. To find a solution for that question they gathered programmers answers and posted this article How to program a simple chat bot AI?
Stack Overflow Q&A site also tried to answer a question: how to realize one-on-one conversation between a human and a chat bot?
As of right now, the only Bots available to add on Skype are Bing Music, Bing News, Bing Images, Getty Images and Build Bot (which is mostly centered around the Build conference).