XDA Developers is a mobile software development community.The sites main purpose is discussion, troubleshooting and development for Android, Windows Phone, Web OS, Ubuntu Touch, Firefox OS and Ti zen phones.
The site also offers Windows Mobile and Android users general information about devices, ROM upgrades, technical support, Q&A, and reviews of device applications and accessories.There are different forum for each model of manufacture smartphone like LG, Samsung, HTC, Motorola, Sony and many others.Most of the time I used this site to flash custom ROM for my Lg optimus G.
This site is very useful if you wanted to root your smartphone, it will give you step by step procedure to root your phone, and if you dont understand anything then you can ask in forum.It also keep you up-to-date from the latest technology.Many software and hardware hacks, rooting methods, and other phone and tablet specific tweaks originate from the members of the XDA Forum.If you are a developer than you can join with other developers to develop something new.