You can trade stocks with a laptop and a brokerage account. You're not going to be able to trade bonds without a Bloomberg Terminal. The killer components are industry standard calculations and nearly universal bond data. There are some proprietary analytics, but they are honestly an add on.
It's a market that should be ripe for disruption, because there are really a limited set of competitors, extracting near monopoly rents. At the same time open source only takes you so far because the data is the issue, and the issue is not market data, but reference data -- stuff that is mostly static, but potentially changing. It takes a lot of work to get that that right. (I worked for a fintech startup which went bankrupt because, among other reasons, we decided to create our own security master database, rather than buying it from a vendor. How hard could it be? Turns out very hard.)