If you use bitcoin and other crypto-currencies for 'day to day' transactions for purchasing or selling goods and services, or as an investment instrument to make a profit; you will be affected by all the price fluctuations in between all the transactions you make 'day to day' or the buy / sell differences during investing activity.
Kryptofolio+tax allows you to import all your transactions from your Bitcoin and Altcoin wallets either via a wallet export to csv or direct from the blockchain or (for extra privacy) a QR Code direct into your smartphone; it will then automatically lookup the historical value of these transactions in your selected fiat currency (USD,GBP,EUR,any other). The tool can then calculate profit and loss for each transaction and keep a running score.
There is a summary screen that tells you your current value and 'cash out' profit or loss, you can use this tool to drive your trading strategy or for calculating the capital gain in-between all these price movements useful for working out tax liability.
As a shorthand on this site and in the app a cryptocurrency is referred to as coin.