I'm really not going to rec K-On! to everyone, promise! But it's totally about girls just hanging out & being friends & rocking out. (There are nods to femslashiness, but I actually think they are fewer & far between-er than most of the fandom wants to believe & I think it's pretty easy to not read them in & just have it be all about friendships.)

... the technical details thing makes me think of, um, pretty much ALL the baseball anime/manga series I've seen. Though baseball may not be your bag at all -- if you are interested I can narrow it down! (I will say lots of people go "I never thought I'd be interested in hearing ppl talk about baseball until -- " but yeah, not for everyone.) Um, although Moshidora in particular has friendship between two girls as the core of the story (around one of them being the manager of the baseball team, & using Peter Drucker's Management as the way she runs the team -- so ticking two boxes).

Kimi ni Todoke's main plot revolves around romance, so you may not be interested, but there's also really awesome stuff about friendship between girls.