I tried Tower when it was in beta for Windows, but the cost is too steep to justify it for me. But it seemed to be a lot more full featured than the GitHub client which isn't good for more than basic commits. And again, no Linux there either.
I'd definitely go for a solid, open source git client, and it's obviously very relevant to GitLab's business.
Seriously, SublimeText, which is $70 closed-source.
Less seriously, macOS and iLife. I'd be ok to pay €200/year/user for an OS of that quality, as long as it's open-source.