Client – I am looking for a software called instawallet which was used as a Bitcoin wallet in 2011.

According to Bitcoin Wiki, Instawallet launched in April 2011 (you’re probably misremembering that it was in March) and was shut down in 2013 after a hack. Because it is a web wallet, there is no software you can download to recover your funds.

The wiki claims that Instawallet users can “submit a claim form to receive funds,” but I couldn’t find a source for this and the website is down anyway, so I’m not sure where to submit that claim.