I want to test Ushahidi platform, is it possible to install it on local server or computer using Denver for instance.
Yes. This is commonly done by developers.
First you need to set up Apache, MySQL, and PHP on your local computer/server. You can do this fairly easily with LAMP for Linux, WAMP for Windows or XAMP for OSX. Google the version for your operating system, download, and install. Then follow the installation instructions that come with Ushahidi.
We’ve published our installation guide on the wiki: https://wiki.ushahidi.com/display/WIKI/Ushahidi+Installation+guide