If your startup is based on a software product, you must develop it and you want to do it in the best way. Besides, if you are (or have) a developers team, you will need to manage tasks, resources, code releases, etc. So, maybe a issue and project tracking like Jira could be really useful [...]
When you have a web-based product or an online service, specially when it has been on creation process yet, you need feedback to know what users want. So you can know the features that people demand on your site and develope it as soon as posible, building your product based on that information. In this [...]
One of the most useful apps for Startups is the suite Google Apps. This service provided by Google company allow using custom domain names with several Google products, including: GMail, Calendar, Talk, Docs and Google Sites.