I have used ShareScope for some years. It is excellent. I ran it initially on a Windows PC and later on a virtual machine provided by Parallels on a Mac.
Reliability and accuracy are faultless. The software is updated regularly and problems dealt with immediately. The support is as good as that provided for any software product I have ever used and better by far than any I can think of. You talk to real people who know their system backwards and are unfailingly patient and helpful. Email problems are dealt with competently, immediately and efficiency. And most of the time, the problems have arisen through my own fault or ignorance.
The database is vast. The system deals with all UK and US stocks and indices. It is updated constantly. There are other services on offer. If you trade stocks, shares, trusts, OEICs and so forth, use this product.