When Bump CEO Dave Lieb decided in his first year of business school to make a mobile app, he started researching the most popular ones in 2008 — fart noises and sideways keyboards.

“It’s a totally different world,” says Lieb, five years later, sitting in his Mountain View office with a counter clocking the total downloads of Bump, his app that lets users share contact info by tapping their phones together. He estimates by Friday morning that counter will read 100 million downloads.

After getting the idea for Bump, Lieb joined Y Combinator, dropped out of business school and never looked back. Bump has raised $20 million in funding to date and this week’s 100 million downloads worldwide will represent yet another milestone.

It’s been a big year with Bump releasing two new iPhone apps in 2012, peer-to-peer mobile payment app Bump Pay and photo-sharing and grouping app Flock, plus Bump 3.0. Instead of adding to the 3.0 release, Bump deleted its calendar, app and music sharing features, leaving only the functions Bump was designed to do, swap contact info and photos

“Those features were interesting, but they never became the larger features. It was muddying the user experience. The problem is it’s hard to have multiple things users can understand about a brand,” says Lieb.

It was contemplating the simplified user experience that brought Bump to Flock. Lieb compares Flock to Pay with Square, Square’s consumer mobile wallet app that runs in the background and allows for a hands-free payment, saying he sought to reduce the action required for photo sharing.

“If you have to remember to use the app, it fails. People won’t change their behavior,” says Lieb.

Flock runs in background, links to Facebook to figure out your friends, uses GPS to determine where and when photos are being taken, then alerts users that it wants to aggregate the photos into a single group album within the app. Instead of tracking down photos via email or mass broadcasting them on Facebook, Flock keeps it in one spot, relevant to the right people. Lieb says 500 million photos are uploaded to Facebook everyday, but that’s only small amount of market. Flock is banking on people looking to share photos through a new, more limited distribution model.

“Every photo was taken to share with someone,” says Lieb. “We say share it with people it’s relevant to.”

Though he wouldn’t talk about when to expect new apps, Lieb says Bump is focused on creating experiences that infer the users intent using location trapping smartphone technology.