Short answer is ToR...
https://www.torproject.org/download/download
Long answer and explanation follows..
So the deal is you can't not say where you are connecting from it's part of the TCP\IP protocol. and the TCP\IP protocol is the backbone of the internet.. What you do is connect to an intermediate service, which makes you appear as coming from the intermediate location rather than your actual location. Then that service handles passing the data from you to the destination and visa verso... There are lots of such services. They come in two flavors.. a VPN.. virtual private networks, proxi servers and then their is ToR...
VPN's are especially useful if you want to watch the latest BBC television season but the BBC website only allows residents of the UK to look at them. Using a VPN service like Tunnel Bear not only allows you to hide that you are in the US but it allows you to appear like you are coming from UK, France, Russia... where ever they have a tunnel bear.end point. You can choose. Since your connection to the VPN is secure, and the VPN's connection to it's endpoint are secure.. This will mask your surfing from everybody except the VPN service provider... Oh and if you want to purchase a linux server... Raspberry Pi for instance for $40 you can set up your own VPN service using all shareware. Or you can pay a nominal fee and use an existing one.. This is kind of a heavy protocol as there is a public private key certificate exchanged and the VPN bassically defaults as your internet connection so all your internet traffic will default to using it once you log in..
The weakness of a VPN is that there is still a single location which knows all.. The VPN itself.. also that VPN ip address is visible to anybody looking at your traffic...
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The other flavor is a proxi server... Proxi servers are lighter weight so it's possible to use more than one of them, or default them like a VPN in your browser settings... Same kind of thing as a VPN only there is no encryption or data sharing component with other members of a VPN, because of coarse there is no VPN. A proxi server is basically a website which you connect too, and then connect through to your final destination. So proxi's are a little less secure.. Good enough to stop web sites or your employer from seeing where you are surfing... all they'll see is you connecting to the proxi..., but if someone is actually sniffing your packets they can defeat the proxi server... The VPN and it's encrypted traffic would hide everything.
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Since you requested a specific "App" your answer is ToR... Originally stood for The Onion Router ( layers inside of layers). Tor directs Internet traffic through a free, worldwide, volunteer network consisting of more than five thousand relays to conceal a user's location and usage from anyone conducting network surveillance or traffic analysis. Using Tor makes it more difficult for Internet activity to be traced back to the user: this includes "visits to Web sites, online posts, instant messages, and other communication forms". Tor's use is intended to protect the personal privacy of users, as well as their freedom and ability to conduct confidential communication by keeping their Internet activities from being monitored. An extract of a Top Secret appraisal by the National Security Agency (NSA) characterized Tor as "the King of high secure, low latency Internet anonymity" with "no contenders for the throne in waiting" Tor is the answer you are looking for...