Typing in IRC will take karma away from an item (e. g. Karmabot) Typing! rank and then an item will let you know how much karma it has (e. g. ! rank Karmabot) Typing! top will list the top 5 items by karma IRC bots can be used for all sorts of tasks. You could simulate another user (by writing a simple AI for example). You could make the bot send certain messages into the channel. In summary to write an IRC bot, open a TCP socket to an IRC server in whatever language you want and start doing stuff.
To write a slack bot, go jump through their hoops and proprietary tech, and maybe they'll let you do stuff. Lets compare writing a bot for Slack with writing an IRC bot. First of all, lets summarize the process for making a Slack bot. Full details are available in their documentation. The basic steps are: Create a Slack account and workspace to host the bot (you may have already done this step). An IRC bot differs from a regular client in that instead of providing interactive access to IRC for a human user, it performs automated functions.
( Source ) So basically, an IRC bot appears as another user to everyone else, but instead performs set actions per its script in response to predetermined events (usually specific messages in the chat).