I use HTC Power to give on my M7 and since i work with used phones i have about 15 other devices running the sister app BOINC.
I just hope all my donated computing power is going to good use.
Check out the BOINIC app. Im not sure how far back its compatible but i have used it on some older and non htc devices.I was actually going to use it on my Droid Razr Maxx after I got an M8 but my Razr Maxx is on 4.1.2 and Power to Give needs at least 4.3. I kind of wish HTC marketed it more, it would go towards a good cause and give HTC more publicity.