One of my extremely geeky hobbies is online singing. There are a number of groups floating around the internet that people can join. Usually, you send in an audition clip and then you are assigned to a group. After that, it works a lot like karaoke. You are assigned certain lines to sing in a song (either in your group or a song you signed up for) and it is your job to record you singing those lines. Right now, the main group I sing with is Sekai no Melody. Unlike many other groups, SnM tries to get away from only recording Japanese songs. As a result, there are groups that focus on other languages as well. (For example, one of the groups I'm in focuses on English songs.)
Yes, I know it is very geeky but it's also a lot of fun!