This series of quickstart guides will show you how decentralized, networked applications can be quickly built and published on Urbit. These guides are intended for developers with limited knowledge of Urbit and who aren't fluent in Hoon (Urbit's programming language). They don't delve deeply into the code, but instead focus on the broader process, to give you a basic idea of the platform. If instead you want to learn Hoon and app development on Urbit, the best place to start is Hoon School, and then after that App School.
There are so-far three guides in this series:
The theme is a suite of apps for groups of people to collaborate and communicate. The groups app is called Squad, and lets you create public and private groups that others can join. The chat app is called Hut, and lets you create chat rooms which members of your Squad groups can join. The third app is called Tally and lets group members create polls, which other members can vote on. Tally uses linked ring signatures so members of a group can verify votes but don't know who voted for what.
These apps are quite basic and are intended as educational tools rather that full-featured apps for everyday use. However, once you have these, they are yours, and you can build or modify them however you (or your team, your DAO, etc) would like.
For the front-ends, the chat app uses React, and the other two use Sail, which is Urbit's native server-side HTML language. Note these are not the only ways to build front-ends: you can also build CLI apps, desktop apps, mobile apps, or use any other browser-based front-end framework, and have them talk to Urbit ships.
If you'd like to try out these apps immediately, you can search for ~pocwet in the search bar of your ship's homescreen, and install them from there.