SQLDeveloper is great, but it has a habit of acquiring more and more memory until your PC starts paging and things grind to a halt. Then you kill it with task manager and things go back to normal again. I wish I had a solution to this.
I installed DBeaver, but it can't download the Oracle drivers - not sure if it is our network or the repository. Unless someone can explain in simple terms how to obtain the correct drivers and how to install them it is no use.
It's your network, usually DBeaver can download the drivers without any problems and packs it here:
You can also download the Oracle JDBC driver and manually add it into the DBeaver Connection.