Edipress developed Estimo that falls into the Books & Reference category. The tool was downloaded and set up by over 100 users and the latest stable release was on Jan 14, 2012. Users rated this application 3.8 on Google Play.
Get the setup package of Estimo 1.1 that is completely free and have a look at users' reviews on Droid Informer. The app can be launched flawlessly on Android 1.6 and above. The app is completely safe to download.