I have been using Odoo for the past 6 months and have been liking it a lot. https://www.odoo.com/ I found the inital setup difficult but once its setup its been working great. I think its designed for a bigger business with more features than ill ever need but its working fine with my small business. Its open source so you can run it on your own server for free if you want. It has an android app but I think its a work in progress. Either way it might be worth checking out.