This app emerged from a mandate to make the caucus more accessible and transparent. It was well-intentioned but underfunded and lacked comprehensive organizational buy-in. Introducing tech can help but you have to spend tons of money to make it reliable and usable, then you have to spend more to train everyone in using it. This is a problem organizations of all sizes and shapes face when making massive IT changes.
Shadow is a firm that makes custom software for Democrats and progressives. It has an unnecessarily sinister name. There are not a lot of companies that make software for Democrats because it’s an awful job. You make very little money. Everyone hates you when things go wrong, which they will, because the product testing cycle and margins are nonexistent. Then everyone will assume things went wrong because you are some combination– you choose– of secretly evil, secretly working for Bernie, secretly working for The Establishment/Hillary (per someone's unpersuasive Imgur post below), or secretly working for Buttigieg.
Others have noted that Shadow also made software for the Buttigieg campaign. If you take my claims above as true, this should be unsurprising to you: a hard market where everyone hates you and no one has money to pay you is not attractive to enterprising software engineers, so there are few firms available to choose.